Adding support for X10 basic commands over xPL

This pull request is based on an email that was sent on the list. The original developer is Roger Simon.

I only did basic testing on this code (as in: I added an item in my mht file and saw it showed up in the web interface and it didn't crash misterhouse).

I think this code is missing default on/off states for X10Basic items?
Verified X10Basic messages are generated.

Confirmed that with the proposed syntax in the mht file the following message is generated when $device->send_on() is called:

[xpl-cmnd/x10.basic: mhouse-mh.misterhouse -> hollie-x10gate.downstairs - on uplight]
Merge pull request #130 from hollie/add_xpl_x10_support

Add xPL x10 basic support (input from Roger on mailing list)