Save meta title and meta desc on post save

Closes #4369
- Renamed `editor-route-base` -> `editor-base-route` to bring it in alignment with the view and controller mixins
- Consolidated editor route code into editor-base-route
- Removed `serialize` from EditorEditRoute, as it reimplemented the ember default
Use nested output style for Sass

References #4389

As a result of https://github.com/TryGhost/Ghost/pull/4389#issuecomment-61637323 the best way to keep everything working nicely is to use the `nested` outputStyle for now.
Create Tags Management Stubs for Ember

closes #4260

- Adds "tags" route inside of the settings routes.
- Adds this route to router.js
- Links the route from the settings.hbs template
- Adds demo tags html in tag.hbs template
- Adds flag for tagsUI
Merge pull request #4385 from novaugust/save-meta

Save meta title and meta desc on post save
Merge pull request #4273 from cobbspur/tags

Create Tags Management Stubs for Ember
Merge pull request #4393 from PaulAdamDavis/sass-nested

Use nested output style for Sass
Update to Ember 1.8.1.

http://emberjs.com/blog/2014/11/04/ember-1-8-1-released.html
Merge pull request #4399 from rwjblue/update-to-1-8-1

Update to Ember 1.8.1.