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
Minor shortcut amends

issue #1463

- disables some of codemirrors default shortcuts to prevent them clashing
- minor cleanup of shortcut listing
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
Merge pull request #4153 from halfdan/4151-tag-order

Fix tag order
Merge pull request #4158 from ErisDS/issue-4157

Fix cache-control header for API routes
Merge pull request #4161 from ErisDS/readme

Updating README with clearer install paths
Merge pull request #4159 from ErisDS/about-image-fix

Adding size param to contrib images
Properly server shared files

refs #3992
- Don't use path.join for URLs
- Cache robots.txt for 1h instead of 1y
Merge pull request #4160 from halfdan/3992-fix-shared

Properly serve shared files
Update PRIVACY.md
Upgrading Casper to 1.1.0