Moves reader comments into its own view controller.

Tapping on the comment icon on the post list or detail take you to the comment list.
Merge branch 'develop' of github.com:wordpress-mobile/WordPress-iOS into issues/2395-separate-comments

Conflicts:
	WordPress/Classes/ViewRelated/Reader/ReaderPostDetailViewController.m
	WordPress/WordPress.xcodeproj/project.pbxproj
Updating pods
Fix block declaration for changes made in the sync helper.
Let ReaderPostDetailViewController inherit from UIViewController

Removes dependency on UITableViewController.
Adds scrollview.
Simplifies constraints.
Implemented adding categories in REST

CategoryService was refactored to make use of RemoteCategory objects.

The add category view controller no longer syncs categories after
creation since REST will already return the new category. When sync is
moved to CategoryService, we need to trigger it after creation for
XML-RPC remotes.
Refactor category creation

If the user tries to create a category with a name that already exists,
let's pretend we just created it and use the existing category instead
of failing.
Moved category syncing to CategoryService

Implemented REST category sync
Force blog sync on blog details view
Sync categories after creation for XML-RPC
Replaces optimize switch with image size slider
Fetch post for comments if it's not set yet and show a header containing an overview of the post it belongs to in the new comment page
Merge remote-tracking branch 'origin/develop' into issue/2528-comment-page-header

Conflicts:
	WordPress/WordPress.xcodeproj/project.pbxproj
Adds support for replying to a specific post.
Adds no results view. Switch to ReplyTextView.

Drops inline composer and comment publisher.
Adds the post header view.
Merge remote-tracking branch 'origin/develop' into issue/2528-comment-page-header
Merge branch 'develop' into issue/2551-category-service
Small bug fixes (introduced in the last commit for adding comment page header) related to getting a single post from server
Don't call weakSelf.managedObjectContext, since some reason it doesn't work