Ember redirect to signup

closes #2779

- adds temporary code to redirect the ember admin to signup if a user doesn't exist.
- done serverside as this makes most sense?
Removed holdover popover code in PostsPostController

Ref #2840
-Removed unused isEditingSettings and isViewingSaveTypes from PostsPostController
Update slug API to work with additional types

Closes #2866
-update slug API to handle users and apps in addition to
 posts and tags
-update existing tests
-add new functional tests for slug endpoint on http api
Enable post deletion from Ember admin

Closes #2849
-wire up delete post action in ember admin
-refactor ember modal dialog
-override RESTAdapter.deleteRecord to workaround Ember expecting
 an empty response body on DELETEs
Merge pull request #2869 from ErisDS/issue-2779

Ember redirect to signup
Merge pull request #2875 from novaugust/popover-cleanup

Removed unused popover code in PostsPostController
Merge pull request #2873 from jaswilli/2849-delete-posts

delete posts from post settings menu
Cache invalidation for post update

closes #2833
- Handle status change of post
Fix error when running Ghost with a socket

fixes #2879
- Syncronously unlink old socket file
Merge pull request #2877 from jaswilli/2866-slugs

Update slug API to work with additional types
Merge pull request #2876 from halfdan/2833-rasperize-cache

Cache invalidation for post update
Merge pull request #2880 from halfdan/2879-socket-issue

Fix error when running Ghost with a socket