Update Ace, remove Tab indent, improve code preferences (scopes under the gear icon)

![screen shot 2014-12-22 at 14 52 31](https://cloud.githubusercontent.com/assets/197573/5525688/36df2024-89ea-11e4-8301-6f98b7d9349b.png)

@henrikengstrom BTW, the tab behaviour does work as I told you: it doesn't update indentation, but sets it for new lines. My opinion is: we keep it as is. Who votes for removing the functionality?
Shouldn't ``theme`` still be available?