feature/reader-comment-activity

This PR removes comments from the reader post detail and shows them in a separate activity that's displayed when tapping the comment icon (both in the detail and list views). Reasons this was necessary:

* Showing and updating comments in post detail was a real battery/bandwidth drain now that the Android app enables swiping between posts in the detail view (where the user may simply swipe between posts looking for one of interest without caring about the comments)
* The scrollbar on post detail indicated the length of the post plus all its comments, so the user never knew how long they had to scroll to simply read the post
* Tapping the comment icon in the list view would simply show the detail view rather than scroll to its comments, and there was no way to resolve this that was user-friendly since comments on a post couldn't be requested until the detail view was shown