Added more granular instrumentation to ADAM

This includes new instrumentation code to measure timing in Spark operations,
as well as instrumentation of the ADAM Transform operation.

When -print_metrics is specified on the command line this produces output like the following:

 ```
Timings
+----------------------------------------------------------------+-------------+-------------+--------+-----------+-----------+-----------+
|                             Metric                             | Worker Time | Driver Time | Count  |   Mean    |    Min    |    Max    |
+----------------------------------------------------------------+-------------+-------------+--------+-----------+-----------+-----------+
| └─ Load Alignment Records                                      |           - |   534.49 ms |      1 | 534.49 ms | 534.49 ms | 534.49 ms |
|     └─ BAM File Load                                           |           - |   522.82 ms |      1 | 522.82 ms | 522.82 ms | 522.82 ms |
| └─ Trim Reads                                                  |           - |    10.32 ms |      1 |  10.32 ms |         - |         - |
|     ├─ adamFirst at TrimReads.scala:117                        |           - |           - |      1 |         - |         - |         - |
|     └─ adamMap at TrimReads.scala:123                          |           - |           - |      1 |         - |         - |         - |
|         └─ map function                                        |   2.02 secs |           - | 163064 |  12.37 µs |         0 |  11.01 ms |
|             └─ Trim Reads                                      |   1.89 secs |           - | 163064 |  11.58 µs |         0 |   9.08 ms |
|                 └─ Trim Cigar                                  |   122.98 ms |           - | 162311 |    757 ns |         0 |   7.29 ms |
| └─ Mark Duplicates                                             |           - |    13.05 ms |      1 |  13.05 ms |         - |         - |
|     ├─ adamGroupBy at SingleReadBucket.scala:31                |           - |           - |      1 |         - |         - |         - |
|     │   └─ groupBy function                                    |    46.08 ms |           - | 163064 |    282 ns |         0 |     57 µs |
|     ├─ adamMap at SingleReadBucket.scala:32                    |           - |           - |      1 |         - |         - |         - |
|     │   └─ map function                                        |   156.13 ms |           - |  81741 |   1.91 µs |         0 |  28.63 ms |
|     ├─ adamKeyBy at MarkDuplicates.scala:75                    |           - |           - |      1 |         - |         - |         - |
|     │   └─ keyBy function                                      |    525.3 ms |           - |  81741 |   6.43 µs |      1 µs |  34.36 ms |
|     │       └─ Create Reference Position Pair                  |   488.06 ms |           - |  81741 |   5.97 µs |         0 |  34.36 ms |
|     ├─ adamGroupBy at MarkDuplicates.scala:75                  |           - |           - |      1 |         - |         - |         - |
|     │   └─ groupBy function                                    |    48.01 ms |           - |  81741 |    587 ns |         0 |    162 µs |
|     └─ adamFlatMap at MarkDuplicates.scala:76                  |           - |           - |      1 |         - |         - |         - |
|         └─ flatMap function                                    |   874.43 ms |           - |  16999 |  51.44 µs |      2 µs |  42.41 ms |
|             └─ Perform Duplicate Marking                       |   857.33 ms |           - |  16999 |  50.43 µs |      2 µs |  42.41 ms |
|                 └─ Mark Reads                                  |   142.56 ms |           - |  73366 |   1.94 µs |         0 |  38.93 ms |
| └─ Sort Reads                                                  |           - |     8.86 ms |      1 |   8.86 ms |         - |         - |
|     ├─ adamMap at AlignmentRecordRDDFunctions.scala:272        |           - |           - |      1 |         - |         - |         - |
|     │   └─ map function                                        |    42.38 ms |           - | 163064 |    259 ns |         0 |     65 µs |
|     ├─ adamSortByKey at AlignmentRecordRDDFunctions.scala:281  |           - |           - |      1 |         - |         - |         - |
|     └─ adamMap at AlignmentRecordRDDFunctions.scala:281        |           - |           - |      1 |         - |         - |         - |
|         └─ map function                                        |    38.31 ms |           - | 163064 |    234 ns |         0 |     83 µs |
| └─ Save File In ADAM Format                                    |           - |    58.83 ms |      1 |  58.83 ms |         - |         - |
|     ├─ adamMap at ADAMRDDFunctions.scala:80                    |           - |           - |      1 |         - |         - |         - |
|     │   └─ map function                                        |    20.92 ms |           - | 163064 |    128 ns |         0 |     13 µs |
|     └─ adamSaveAsNewAPIHadoopFile at ADAMRDDFunctions.scala:82 |           - |           - |      1 |         - |         - |         - |
|         └─ Write ADAM Record                                   |   5.43 secs |           - | 163064 |  33.29 µs |         0 | 1.13 secs |
+----------------------------------------------------------------+-------------+-------------+--------+-----------+-----------+-----------+

Spark Operations
+---------------------------------------------------------+--------------+------------+----------+
|                        Operation                        | Is Blocking? |  Duration  | Stage ID |
+---------------------------------------------------------+--------------+------------+----------+
| adamFirst at TrimReads.scala:117                        | true         |     562 ms | 0        |
| adamMap at TrimReads.scala:123                          | false        |          - | -        |
| adamGroupBy at SingleReadBucket.scala:31                | true         | 10.14 secs | 2        |
| adamMap at SingleReadBucket.scala:32                    | false        |          - | -        |
| adamKeyBy at MarkDuplicates.scala:75                    | false        |          - | -        |
| adamGroupBy at MarkDuplicates.scala:75                  | true         |  6.61 secs | 3        |
| adamFlatMap at MarkDuplicates.scala:76                  | false        |          - | -        |
| adamMap at AlignmentRecordRDDFunctions.scala:272        | true         |  9.52 secs | 4        |
| adamSortByKey at AlignmentRecordRDDFunctions.scala:281  | false        |          - | -        |
| adamMap at AlignmentRecordRDDFunctions.scala:281        | false        |          - | -        |
| adamMap at ADAMRDDFunctions.scala:80                    | false        |          - | -        |
| adamSaveAsNewAPIHadoopFile at ADAMRDDFunctions.scala:82 | true         |  9.05 secs | 1        |
+---------------------------------------------------------+--------------+------------+----------+
```

Some notes:

* Sorry for the gigantic PR! I got a bit carried away. However, most of the changes should be isolated to the  instrumentation package, so hopefully it's not too much of a pain to review.

* I have instrumented the ADAM Transform command. Therefore there are quite a few files changed in the core ADAM code, but these changes should be isolated to changing RDD operations to use the instrumented version, and addition of timers.

* The approach that I've taken is to wrap each Spark RDD operation in an instrumented version. For example, to instrument `map` operations we use the `adamMap` operation instead, which is the instrumented version. 

* Some of the code for instrumenting Spark RDD operations needs to go in the org.spark.rdd package for now, which is clearly a bit weird. This is so that Spark uses the correct call-site (and therefore stage name). I believe that this can be changed when we upgrade to Spark 1.1.1, which includes SPARK-1853 -- this fixes an issue with overriding call-sites. Instead of using the org.spark.rdd package we can just override the call-site instead.
Is it possible to reset the generator? Seems like that might be a preferable option.