Added more converters, extra LockScreen methods and a behaviour

Added three new converters:
EnumToBooleanBaseConverter
GreaterThanVisibilityConverter
LessThanVisibilityConverter

Added two extra methods to the Lock Screen Service that allows you to set the default lock screen and set the lock screen providing a url, if it's an http url it will download the image and save it in isolated storage.

Added SystemTrayProgressIndicatorBehaviour
This behaviour lets you have your own colour as the progress indicator in the system tray, rather than the phone's accent colour. Demo of it in use: http://youtu.be/KhmcqDlfZSM