New Post UX behaviour.

refs #1351
- Make generateSlug a static method on base model
- Change client behaviour (unfinished)
- Add new getSlug API method
Extending halfdan’s work for UX settings improvements

#1351

- prevent a new post (not saved on server) from
updating its slug/date to the server

- fix jshint

- add back creation of a posts slug upon a post creation

- update for rebasing

- hide ability to ‘delete this post’ from post settings
menu when a post hasn’t yet been saved to the server
Merge pull request #1839 from hswolff/1351-post-settings-ux

New Post UX behaviour.