Added setter method setGenerator to JavaRDD.
Added mapPartitions method to JavaRDD.
Added foreachPartition method to JavaRDD.
Remove classtag from mapPartitions.
Remove default param from mapPartitions
Modifications as suggested in PR feedback-

- mapPartitions, foreachPartition moved to JavaRDDLike
- call scala rdd's setGenerator instead of setting directly in JavaRDD
Modifications as suggested in PR feedback-

- more variants of mapPartitions added to JavaRDDLike
- move setGenerator to JavaRDDLike
- clean up
fixed ClassTag in mapPartitions
Merge branch 'java-api-completeness' of https://github.com/ScrapCodes/incubator-spark into java-api-completeness
clean up as suggested in PR comments
Test suites for filterWith, and added filterWith to Java(Double|Pair)RDD.
Used Integer instead of scala.Int, which forces JavaApi user to import scala Int.