Minor code style corrections.
Styles reader comment cells
Optimize avatar loading for reader comments.

Fixes an issue where a gravatar url missing a hash would cause an exception in WPAvatarSource.
Adds the default identicons to the project vs fetching them.
Layout changes. Limits nesting to 3 levels.
Merge branch 'develop' into issues/990-reader-comment-improvements

Conflicts:
	WordPress/Classes/ViewRelated/Reader/ReaderPostDetailViewController.m
Merge pull request #1718 from wordpress-mobile/issues/990-reader-comment-improvements

Issues/990 reader comment improvements
Merge remote-tracking branch 'upstream/develop' into develop