classes/[gnome|gnomebase|mime]: enhance gnome related classes
This patch pulls in the gnome related classes from oe-core which
adds extra packaging rules and functionality whilst modularising things
so that one can get a subset of gnome functionality without adding a lot
of extra dependencies.
These aren't an exact copy of the classes from meta-openembedded, notable
differences are:
* gnome.bbclass - I dropped the BBCLASSEXTEND
* mime.bbclass:
- updated coding style
- use which to find update-mime-database program rather than hard coded
- fix typo in populate_packges_append such that it's actually called
