Adds mentions to reader comment replies (both if you transition first into a particular post to reply OR for replies directly from the reader).
Add progress report for media uploading.

Use NSProgress to report uploading progress.
Add NSProgress to interface of MediaService.
Fix error callback calls and make them use current queue instead of main one.
Improved documentation of MediaService.
Better fix for relative URLs
Cleans up the editor's Blog object handling.
Removed an unnecessary file.  Code cleanup.
Add progress reporting for setting featured image.
Only increase size by 1 to avoid show incorrect size of file.
Add progress reporting view controller to legacy editor.
Replace cancel button for done button.
Several improvements to our new editor.
Several improvements to the code to handle saving posts.
Use path instead of NSManagedObjectID for persistance.
Fixes some issues with the pages editor.
Fixed a logic error saving a removed post's context.
Merge commit '9bba5a9a58aeaef5968255e766d9489a65294326' into issue/2699-add-mentions-to-reader-detail-replies

Conflicts:
	WordPress/Classes/ViewRelated/Reader/ReaderCommentsViewController.m
Simplify constraint code into a single VFL call props @aerych
Instead of adding and removing the off-keyboard gesture recognizer, let's just enable and disable it as needed.  Props @aerych
always set viewHeight to UIScreen mainScreen height so that WPNUXUtility can center controls vertically