Added X10 support to the InsteonPLM binding

The PLM modem supports sending and receiving legacy X10 messages. There are a significant number of X10 devices installed.

This pull request enhances the binding to allow openHAB users to interact with X10 devices via the PLM. The modifications have been tested with an X10 switch, dimmer, and a motion sensor. Regression testing has been performed to ensure the functionality of Insteon devices is not impacted.