Implement a Generic Uploader - #2886
Fixed publish button not updating with model  change

Closes #2908
- Changes `willPublish` from `oneWay` property to computed property.
Merge pull request #2886 from lholmquist/wrap_uploader

Generic Uploader component
Merge pull request #2909 from novaugust/publish-button-reset

Fixed publish button not updating with model  change
Split PostController amongst new Editor/PostSettingsMenu Controllers

closes #2910
- create EditorController, PostSettingsMenuController
- remove `posts.post` controllerName dependency on EditorRoute/NewRoute
- `{{render}}` the PostSettingsMenuView with its own controller
- break up properties/methods from PostsPostController into all three controllers
- fix EditorRoute pagination options to now be comparable to PostsRoute
- add NewController to force NewRoute to refresh editor with blank model. Identical to Editor's
- EditorController and NewController are based on a shared mixin
- NewView created, templateName is 'editor'