[Core] Upgrading ScalaStyle version to 0.5 and removing SparkSpaceAfterCommentStartChecker.

Author: prudhvi <prudhvi953@gmail.com>

Closes #2799 from prudhvije/ScalaStyle/space-after-comment-start and squashes the following commits:

fc263a1 [prudhvi] [Core] Using scalastyle to check the space after comment start
topic modeling on Graphx
Refactoring sampling process
Optimizing Performance
Refactoring perplexity method