Add Gmail-style shortcuts

Ref #3940
- add `j`/`k` for navigating posts down / up
- `c` for opening a new post
-  `o` to open the selected post
- update keymaster dep to allow for multiple key unbinds (`key.unbind('up, j')`)
Fix GhostTab and GhostTabPane array dependencies

No issue
- TabPanes weren't finding their tab due to not listing all their dependencies in Ember.computed
Implements setting specific body classes

closes #4116
- Adds css classes to settings views
Minor shortcut amends

issue #1463

- disables some of codemirrors default shortcuts to prevent them clashing
- minor cleanup of shortcut listing
Enable cycling header levels with ctrl+h.

closes #3019

* Remove preexisting `ctrl+h` keymap.
* Add logic to cycle the header level.
  * Loops around after h3.
  * Sets cursor position to end of heading
  * Set initial level to h2.
* Remove `ctrl+alt+${NUM}` keymaps (as they do not work
  internationally).
Updating markdown help modal with new shortcuts

issue #3019
Undisable nProgress

Closes #4095

* Removes the line that killed nProgress for PSM
* adds to styles to make nProgress appear again (ht @halfdan)

IRC: http://107.20.237.151:8081/logs/%23ghost/20140922#pm51214
Merge pull request #4145 from ErisDS/pr/3484

Enable cycling header levels with ctrl+h.
Merge pull request #4120 from halfdan/4116-settings-classes

Implements setting specific body classes
Merge pull request #4096 from javorszky/enable-nprogress

Undisable nProgress
Version bump to 0.5.2-rc1
Minor style fixes

no ref
- fix .featured/.unfeatured padding
- fix settings cog padding
Updating README with clearer install paths
Fix tag order

fixes #4151
- Properly re-add pre-existing tags to beginning of array
Rename helpers/ghostPaths.js -> helpers/ghost-paths.js

Refs #4144
Update top-gh-contribs to get contributors within last 90 days

Closes #4130
Merge pull request #4154 from tundal45/ghost_path_rename

[WIP] Rename helpers/ghostPaths.js -> helpers/ghost-paths.js
Merge pull request #4156 from novaugust/iss4130

Update top-gh-contribs to get contributors within last 90 days
Adding size param to contrib images

no issue
- reduces filesize significantly, whilst not impacting quality
Fix cache-control header for API routes

closes #4157

- adds cache-control header back to api routes
- moves cache rules object into testUtils
- adds cache-control header test to every existing API test