Add support for off_fast and on_fast to SwitchLinc Relay

This allows the SwitchLincRelay to process the off_fast and on_fast commands generated with a double-tap.  It's useful to be able to activate scenes, timers, etc. with the double-tap vs. a single-tap.

The  derive_link_state routine is copied from BaseInsteon, and then merged with the link_state set code from the Insteon::DimmableLight routine.