[LightDM] Greeters now split out from LightDM daemon branch

[Robert Ancell]

Hi all,

I've just split the GTK and Qt reference greeters into their own
projects (http://launchpad.net/lightdm-gtk-greeter,
http://launchpad.net/lightdm-qt-greeter).  The branches are
lp:lightdm-gtk-greeter and lp:lightdm-qt-greeter.

The reasons for splitting out the greeters:
- The project is mature enough now that there are other greeters
available to use.
- They are developed at a different pace to the core daemon
- The APIs are stable, and are have extensive regression tests
- This allows others who may have an interest in these greeters to
take control of their development.

Thanks,
--Robert