Add a new theme flag - library.  Not directly available to be used itself but
installed as a lib for other themes.  Like SDL, or GTK.

Get rid of mobility - it's better done with Comanche and schemas.

Describe themes instead of restricting them.  Mobile themes can be used as
the desktop theme and vice-versa.  This deals with the problem of "but my
device is something inbetween".

Presently not exposed to members.
Merge pull request #686 from beardy-unixer/master

Add a new theme flag - library.  Not directly available to be used itsel...