Add error template, route and controller

closes #2851

- adds asset paths to ghostPaths as we don't have an asset helper
- sends any invalid routes to 404
Implement Mobile Editor

closes #2957
- add FastClick library to Gruntfile.js
- add touch-editor to client/assets/lib/
- add mobile-specific utils to util/mobile-utils.js
- add codemirror util to set up TouchEditor only if we're really on mobile
- change gh-codemirror from having a default action to a named action. prevents Ember.TextArea firing action on change
- change gh-codemirror `cm.getDoc().getValue()` to `cm.getValue()` for portability
- change codemirror-shortcuts ES6 export/import style
- changed ghostimagepreview.js to check for Ember.touchEditor in addition to Ghost.touchEditor
Mobile Interactions

closes #3018
- split clientold mobile interactions into their respective Ember routes/views
- create PostsView and SettingsView with mobile interactions
- place interactions for the publish bar into ApplicationRoute on init
Merge pull request #3089 from halfdan/app-slug

Generate slug when adding new app.
Merge pull request #3050 from darvelo/mobile-editor

Implement Mobile Editor
Merge pull request #3055 from darvelo/mobile-interactions

Mobile Interactions
Merge pull request #3052 from ErisDS/issue-2851

Add error template, routes and controller
Set edit post shortcut to 'enter'

closes #2308
Finish Debug screen for Ember admin

Closes #2847
Merge pull request #3091 from jaswilli/debug

Finish Debug screen for Ember admin
Add vertical table alignment class
Prevent cover image `<img>` having a max height.
Allow tabbing responsive editor when not on mobile.

fixes #3095
- Add `click` event to floatingheader
Fix tags UI issue

Closes https://github.com/TryGhost/Ghost/issues/2491 & #27

- Adjust the widths of the tags wrapper element and move gradient to
the edge of said wrapper
Merge pull request #3098 from halfdan/3095-non-mobile-tabbing

Allow tabbing responsive editor when not on mobile.
Stay on posts.index route when no posts exist

No Issue
Remove extra shadow & left border on post settings button

Closes #49

- Remove shadow from the post settings button
- Remove left border from split buttons globally
Merge pull request #3104 from jaswilli/route-undefined

Stay on posts.index route when no posts exist
Stop Markdown help icon from moving

No issue

The markdown help icon would move when `<body>` gets a class of
`editor`. The class wasn't needed, so it's gone from the selector now.
Add off as a noop function to touch editor.

Closes #3107