Revert "Merge pull request #2284 from jaimeiniesta/patch-1"

This reverts commit a6b88d1e7e3fdb41e425d1a285dc7a73788d491b, reversing
changes made to 9bee0b6e2d60e61df136b81261110cc7dcccc52c.
Add filters to colors ui
Update translations
Version bump to v0.9.9.3
Update onebox gem - don't show github.com twice in succession
Improved Plugins SCSS management

 - Moves the import of plugins for both mobile and desktop from common after discourse loading, allowing plugins to overwrite
 - Make desktop-option behave like the mobile-option: SCSS/CSS marked with that option will only be loaded for desktop from now on and ignored in mobile
 - Add variables-keyword, allowing plugins to ship and overwrite variables before they get imported by discourse (great for theming)