Allow devices without options to be created.
Add initial support for Philips amBx lighting devices.

At the moment, assume a single device per system; we currently only
expose a method to set a static colour, but there's a more exciting
timed colour sequence one to come.
Expose amBx control method on Controller.
No reason for this to be a static method.

It has nothing to do with its parent class...
Handy "all off" method.
Tidy up some comments.
Allow optionally specifying a device number for amBx devices.

This theoretically allows support for more than one - no idea how one is
supposed to tell them apart though!