Lock Screen in Precise Now Uses LightDM, More

Some new improvements to LightDM and Unity Greeter have landed into precise.

The greeter theme has got some eye candy and now looks more integrated with overall Unity interface.

Lock screen now uses lightDM greeter.

Lock screen currently looks exactly same as login screen so users can get confused. May be some new changes will land in future updates distinguishing lock screen theme from login greeter.