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.
On my Moto G the animation is pretty chunky, I think because it's doing so much (scale out, hide action buttons, animate in undo bar). Might be worth some optimizations. I can get you a video if you wanna see it.