Fixed Up Actions for CommentListActivity and PostListActivity

When user opens a CommenListActivity from an intent filter
-Up action will load PostListActivity with the appropriate subreddit from the comments url link

When user opens PostListingActivity from intent filter
-Up action will bring user to MainActivity instead of just closing the application
Merge pull request #94 from andrewgiang/master

Fixed Up Actions for CommentListActivity and PostListActivity