Updated stats for Reader.

* Added category to the infinite scroll stat.
* Added "Reader - Unliked Post" stat.
Fixed cell selection bug on notifications view controller.

Fixed a bug where when the user opened a notification's details the
cell would remain selected after returning from the detail view.
Deselect rows on appear for WPTableViewController
Fix cleared image when post is liked

Calling `configureCell:` when the results controller updated the cell
was resetting the image to the placeholder, but the cell still thought
the correct image was set, so any subsequent calls to
`setFeaturedImage:` would be ignored.

resolves #41
Merge branch 'release/3.7' into develop
Revert 589da8 since it was taken care of in 3.7
Fix crash when adding blogs

When the user only had one blog and it's already added, trying to add
more wp.com blogs might result in a crash.

`refreshBlogs` was called on `viewWillAppear`, and it might end before
the view is fully presented. This results in popping the view controller
while it's still being animated and crashes.

Call `refreshBlogs` from `viewDidAppear` instead so the animation is
completed.