Zwave endpoint default to zero

Currently endpoint 1 is assumed as the default. This has an impact with the way messages are sent by the binding since the binding cannot send multinstance encapsulated messages for endpoint 1. This is incorrect - endpoint 1 is a valid endpoint (zwave defines endpoints starting at 1) and it should be possible to send messages encapsulated as multi_instance messages. So, the binding will be changed to use 0 as the default - this will clearly differentiate between the "root" endpoint within the device, and the multi_instance endpoints.