EditPostViewController implements WPEditorViewController from WordPress-iOS-Editor pod

Fixes #1806 

This PR moves the core editing functionality into the WordPress-iOS-Editor pod. The existing editing functionality should remain unchanged (for now) with the exception of the make-a-link dialog:

![screen shot 2014-06-10 at 2 50 06 pm](https://cloud.githubusercontent.com/assets/154014/3235969/7b8a5352-f0d8-11e3-9087-c9d2e98f1e6a.png)

it now uses a standard, two field UIAlertView. There are dependencies to WordPress-iOS-Shared, UIAlertView+Blocks, and CocoaLumberjack (see the podspec).

* Link to pod repo (it contains a stand alone demo): https://github.com/wordpress-mobile/WordPress-iOS-Editor
* Link to published podspec: https://github.com/CocoaPods/Specs/blob/master/Specs/WordPress-iOS-Editor/0.1.3/WordPress-iOS-Editor.podspec.json
The call to remove keyboard observers was duplicated in the original source, but it would be nice if we could clean it up for the pod.