Change logging backend of SLF4j from Logback to Log4j for better compatibiltiy with YARN.
We'll still ship the Logback configuration file and pass them their path to the JVM so that
users can use Flink with Logback as well.

This closes #125
Removed slf4j-simple dependency from streaming component.
Fix Bug in ScalaAggregate Operator and add ITCase
Change Partition Operator to actual general-purpose Operator

It is no longer a special-case operator that can only be used in front
of map-style operations.
[FLINK-1123] Add first-n to Scala API
[FLINK-1120] Add Explicit Partition/Rebalance Operator for Scala API
Update doc with Scala First-N and Partition/Rebalance
[FLINK-1005] Extend TypeSerializer interface to handle non-mutable object deserialization more efficiently.
[FLINK-1005] Add non-object reusing variants of key-grouped iterator.

Clean minor javadoc errors.
[FLINK-1005] Make GroupReduce configurable to use either mutable or immutable object mode