Backend Filtering

This pull request adds publish filtering to the core. 

@andrewminton, @brendo, @designermonkey, there are still a few general issues:

- [x] we need to think about the right variable names, see [content.publish.php#L22-L24](https://github.com/symphonycms/symphony-2/blob/2da1a906a6e5df689ee5d0b6115719adf8798352/symphony/content/content.publish.php#L22-L24)
- [x] incompatibilies should be set on a field level in my eyes, see [content.publish.php#L21](https://github.com/symphonycms/symphony-2/blob/2da1a906a6e5df689ee5d0b6115719adf8798352/symphony/content/content.publish.php#L21)
- [x] <del>filtering options should be added to the Symphony options along with the other environmental information, see [class.administrationpage.php#L351-L378](https://github.com/symphonycms/symphony-2/blob/integration/symphony/lib/toolkit/class.administrationpage.php#L351-L378), which leads to the questions if all functions are in the right file at the moment</del> _see below_
- [x] styles should not use an id selector
- [x] script initialisation should be added to `backend.views.js`
- [x] fix gradients that are messed up by Autoprefixer
- [x] load options asynchronously
- [x] add back arrows to selects