Settings panels are now static

[Bastien Nocera <hadess hadess net>]

Heya,

This afternoon I committed a cleanup of the control-center panels which
mean that:
- panels are now statically compiled into the shell
- desktop files that the panels install must match the
gnome-NAME-panel.desktop
- Bluetooth panel's launcher was renamed to
gnome-bluetooth-panel.desktop
- Remove custom marshallers

This gains us about 1500 lines of code, makes the control-center quicker
to start up, and doing less I/O.

Cheers