Issue/1730 reader detail infinite scroll with blocking

Fix #1675 and fix #1730 - adds "infinite" scroll to the reader detail ViewPager and adds the ability to block a blog from the same view. This was initially submitted as separate PRs, but they rely so heavily on each other that it made more sense to combine them.
Yes, a video would be helpful. Perhaps it would help if I don't show the undo bar until the post finishes animating out?