Insteon:  Add Initial Support for Linking i2cs Devices in MH

No longer do you have to manually link i2cs devices.

Added: enter_linking_mode()

Places the object into linking mode as if you had held down the set button on the device.  To create a link wherein the PLM is the controller, first run the PLM voice command "initiate link as controller". Then run this command.  Finally, run the voice command "scan link table" on this device.

This will eventually be merged into a simpler one-step method, however that will require some additional coding.
Merge pull request #213 from krkeegan/insteon_i2cs_linking

Insteon:  Add Initial Support for Linking i2cs Devices in MH