issue/2121-reader-follow-button-color

Fix #2121 - I wasn't able to reproduce the problem, but I'm pretty sure it was due to my passing the current post to the method that changed the follow button state combined with the way the button's selection state was changed (both fixed in commit 6df0a78 ). While I was at it, I fixed a similar problem with liking and re-wrote the follow button animation (something that has bothered me for a while!).