Global, persistent, per-pad View-Settings

This adds a set of settings which are synchronized for all users, persistent in the database and per-pad.

It looks like this: (updated)
![img](http://i.imgur.com/IPgodJw.png)

Kinda related to https://github.com/ether/etherpad-lite/issues/918
Ready to be **tested** for bugs and usability.