Mce should not depend on maemo

[IMbackK]

1. make devlock/tklock a moudle
   • removes hard dependency on systemui
2. make mce-dmse a module
   • not strictly necessary
3. add xdglock module that calls the xdg mechanisum to summon the lock screen
   • allows use of any lock application (xscreensaver, i3lock etc)
4. Make the build system work without systemui