[SPARK-1853] Show Streaming application code context (file, line number) in Spark Stages UI

This is a refactored version of the original PR https://github.com/apache/spark/pull/1723 my mubarak

Please take a look andrewor14, mubarak

Author: Mubarak Seyed <mubarak.seyed@gmail.com>
Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #2464 from tdas/streaming-callsite and squashes the following commits:

dc54c71 [Tathagata Das] Made changes based on PR comments.
390b45d [Tathagata Das] Fixed minor bugs.
904cd92 [Tathagata Das] Merge remote-tracking branch 'apache-github/master' into streaming-callsite
7baa427 [Tathagata Das] Refactored getCallSite and setCallSite to make it simpler. Also added unit test for DStream creation site.
b9ed945 [Mubarak Seyed] Adding streaming utils
c461cf4 [Mubarak Seyed] Merge remote-tracking branch 'upstream/master'
ceb43da [Mubarak Seyed] Changing default regex function name
8c5d443 [Mubarak Seyed] Merge remote-tracking branch 'upstream/master'
196121b [Mubarak Seyed] Merge remote-tracking branch 'upstream/master'
491a1eb [Mubarak Seyed] Removing streaming visibility from getRDDCreationCallSite in DStream
33a7295 [Mubarak Seyed] Fixing review comments: Merging both setCallSite methods
c26d933 [Mubarak Seyed] Merge remote-tracking branch 'upstream/master'
f51fd9f [Mubarak Seyed] Fixing scalastyle, Regex for Utils.getCallSite, and changing method names in DStream
5051c58 [Mubarak Seyed] Getting return value of compute() into variable and call setCallSite(prevCallSite) only once. Adding return for other code paths (for None)
a207eb7 [Mubarak Seyed] Fixing code review comments
ccde038 [Mubarak Seyed] Removing Utils import from MappedDStream
2a09ad6 [Mubarak Seyed] Changes in Utils.scala for SPARK-1853
1d90cc3 [Mubarak Seyed] Changes for SPARK-1853
5f3105a [Mubarak Seyed] Merge remote-tracking branch 'upstream/master'
70f494f [Mubarak Seyed] Changes for SPARK-1853
1500deb [Mubarak Seyed] Changes in Spark Streaming UI
9d38d3c [Mubarak Seyed] [SPARK-1853] Show Streaming application code context (file, line number) in Spark Stages UI
d466d75 [Mubarak Seyed] Changes for spark streaming UI