Implement Shortcuts in Ember

Closes #2988, #2752
Ref #1463, #2984,
 # Shortcuts via Keymaster
- Added KeyMaster to bower dependencies. KeyMaster is a minimal keyboard
  shortcuts library.
- Added `ShortcutsRouteMixin` for routes that will use shortcuts.
  Currently, only routes can have shortcuts. See the extensive comment
  at the top of `core/client/mixins/shortcuts-route.js` for a
  description of how to implement shortcuts.

 ## Other Changes
- Injected popover service into ApplicationRoute
- Created `EditorRouteBase` mixin for the `editor.new` and
  `editor.edit` routes to mixin.
- `StyleBodyMixin` now calls `this._super()` on `activate` and
  `deactivate` to play nicely with other mixins.

 ## Shortcuts and Stubs implemented
 #### Application-Wide
- `'esc':'closePopups'` shortcut **stub** to close popovers,
 modals, and notifcations

 #### Editor Shortcuts
- `'ctrl+s, command+s': 'save'` note that `command` is the
  `meta` key.
- `'ctrl+alt+p': 'publish'`
- `'ctrl+alt+z': 'toggleZenMode'`
Add Validations Layer and Post Validations

closes #2893, issue #2850, issue #2856
- this is a stable, but quick and dirty validations layer for the time constraints
- this could be replaced with a unified server/client layer later. the infrastructure is there.
- create a validation engine mixin to match validators with models
- override the save method in the mixin to perform validations first
- create a post validator
- fixup calls to .save() to make sure they catch errors properly
Merge pull request #3002 from novaugust/shortcuts

Implement Shortcuts in Ember
Improving Casper test error reporting
Merge pull request #3003 from jaswilli/issue-2846-settings

Convert general settings page to ember data
Merge pull request #3011 from darvelo/validations

Add Validations Layer and Post Validations
Merge branch 'master' of https://github.com/TryGhost/Ghost