Removed tbl_tag_updates, no longer storing before/after fields, no longer passing &after param when requesting newer posts
Remove backfill when updating posts - it didn't work well and wasted bandwidth
Removed UpdateResultAndCountListener
Simplified logic for reporting when posts are updated
Removed irrelevant comment
Removed unused imports
Posts in "Blogs I Follow" are no longer purged when followed blogs change
Rewrote logic for purging posts to discard older posts on a per-tag basis
Code cleanup
Modified UpdateResult to differentiate between when there are new posts/comments and when there are changed posts/comments.
Smarter logic for determining when downloaded posts are new or changed
Response from updating posts in a blog now handled in separate thread
Consolidated response handling when updating posts with a specific tag and updating posts in a specific blog
Merge branch 'develop' of https://github.com/wordpress-mobile/WordPress-Android into issue/1938-reader-update-logic
Now only retaining as many posts per tag as are requested
Posts are now only purged if there's an active connection
Merge branch 'develop' of https://github.com/wordpress-mobile/WordPress-Android into issue/1938-reader-update-logic
Merge pull request #1939 from wordpress-mobile/issue/1938-reader-update-logic

Issue/1938 reader update logic