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
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
Fix invisible tag delete icon
Update README.md

Added a link to dev.ghost.org
Merge pull request #4149 from halfdan/style-fixes

Minor style fixes
Merge pull request #4166 from JohnONolan/tag-icon-fix

Fix invisible tag delete icon
Correct broken Google webfont in editor

Fixes #4162
Merge pull request #4167 from JohnONolan/editor-fix

Correct broken Google webfont in editor
Merge pull request #4147 from ErisDS/shortcuts

Minor shortcut amends
Version bump to 0.5.2-rc2
Close mobile menu on tap.

fixes #4168
- Listen to tap event
Merge pull request #4169 from halfdan/tap-close

Close mobile menu on tap.
Upgrading Casper again
Version bump to 0.5.2