[WIP] SPARK-2360: CSV import to SchemaRDDs

Implements RFC 4180 for parsing comma separated value files into Schema RDDs, which includes:
* Optional header line
* Handling quoted fields
* Handling new lines inside quoted fields

Adds two new methods to SQLContext
* csvFile: Takes a path and returns a SchemaRDD
* csvRDD: Takes an RDD[String] and returns a SchemaRDD

__TODO:__
* Every field is assumed to be of type String. We can either infer types (using a sample of data) or let user specify types of columns.

Can we use an existing tokenizer such as http://commons.apache.org/proper/commons-lang/javadocs/api-3.1/org/apache/commons/lang3/text/StrTokenizer.html ?

We already depend on commons-lang in Spark.