Ember editor save and publish button functionality

Closes #2747
- Added new 'editor-save-button' view and template.
- Added save action to post controller.
- Set a new post as the default model for the /editor/ route.
- Set the `posts/post` controller as the controller for the /editor/
  route.
- Needs ghost-popover #2418 component for full pop-up functionality
Add active class to settings tabs

Closes #2751
Fix default user cover on settings pane

Closes #2806
- Ensures that the user's cover property is a string, otherwise uses the
  default cover.
Update ember post fixture data.

closes #2803
- corrected status published string
- corrected page to not use invalid choices
- updated id integer to start at 1 and not 0
- updated to repeat 31, added a note about removing post id:0
Merge pull request #2810 from shindakun/fixtureupdate

Update ember post fixture data.
Merge pull request #2804 from novaugust/ember-settings-currently-active-pane

Add active class to settings tabs
Merge pull request #2786 from novaugust/ember-editor-save-and-publish

Ember editor save and publish button functionality
Merge pull request #2807 from novaugust/ember-user-cover-default

Fix default user cover on ember settings pane
Refactore slug API for generating tag and post slugs.

Closes #2601
- Removed slug generation from the post API
- Added new, self-contained slug API
- Fixed slug permissions in the fixtures files
- Added a HTTP route for the new API method
- Added integrational tests
Fix up url helper unit tests

Closes #2817
-use async semantics for tests
-fix api.settings.read stub for the url helper describe block
-rename test to describe actual behavior (return '/' instead of '')
Merge pull request #2818 from jaswilli/issue-2817

Fix up url helper unit tests
Merge pull request #2814 from lennerd/issue-2601

Refactore slug API for generating tag and post slugs