Zwave scene controller

This implements the SCENE_ACTIVATION command class. It allows scene controllers to send scene commands to openHAB.

Binding string looks like -:
zwave="14:1:command=SCENE_ACTIVATION,scene=11,state=1"

The scene= sets the scene ID sent by the controller (normally associated with a button).
the state= sets what the binding will send to openHAB.

Since the binding only supports a single string per item, so it's not possible to set more than 1 state for different scenes on the same item like follows -:
{ zwave="14:1:command=SCENE_ACTIVATION,scene=11,state=1" zwave="14:1:command=SCENE_ACTIVATION,scene=12,state=0"  }

The above would be nice since it would allow a scene controller to directly set an item 'properly'. With the current implementation, pressing a scene button will update the item with the set state and this can be used to trigger a rule which is really what a scene controller is meant to do :)