Move editor options to a new page

[Dave Shoreman]

Create a new page (perhaps a user profile) with a section for Editor Settings.

This new Editor Settings section should contain options for setting the default theme and whether to enable line wrapping or not.

Maybe we can keep the theme and line wrapping options in the editor, but they wouldn't really be necessary. Depends if there's anything else that could take their place. The language mode dropdown would be useful to keep in case autodetection doesn't work properly.