fix mirrored scrolling in markdown editor

issue #2426
- ember markdown component now looks for preview element as a DOM ancestor rather than a descendent
Implement signup in Ember

Closes #2410

- Add signup action that posts to signup endpoint
- Fix nav bar showing on signup page
- Fix image link when a user hasn't set their image yet
- Redirect to the ember/signin page if requesting an ember page
Fix content preview actions and add tests

Closes #2798
-fetch full model for active post in Backbone content preview view
-remove unnecessary type check in Models.Post.saving
-add functional tests for all post settings menu actions in editor screen
-add functional tests for all post actions in content preview
 screen for posts with and without tags
Improve status codes

closes #2187
- added UnsupportedMediaTypeError (code: 415)
- added status code 201 if a new object was created
- Updated tests
Add ghostPaths util and initializer

No Issue

- Move the ghostPaths from base model to utils
- Add initializer that injects it into every route, model and controller
- Add a adminUrl and apiUrl helper method
Merge pull request #2768 from jgable/emberPaths
Merge pull request #2754 from sebgie/issue#2187

Improve status codes
correct settings.edit call signature for installedApps

closes #2773

- this is left over from my refactoring work
Merge pull request #2801 from ErisDS/issue-2773

correct settings.edit call signature for installedApps
Merge pull request #2780 from jgable/ember-signup

Implement signup in Ember
Merge pull request #2795 from appleYaks/fix-editor-scroll

fix mirrored scrolling in markdown editor
Merge pull request #2799 from jaswilli/issue-2798

Fix content preview actions and add tests