Support additional listening modes

[jorgh6]

This enhancement will discover supported 'listening modes' when they are first selected on the receiver.

[jorgh6]

I've updated the code, needs further enhancements, but it's working.
Listening modes are added as [xy] New. (where xy is the code transmitted by the receiver)
As long as the square brackets and it's contents are left unchanged, it works. You can replace 'New' with a proper listening mode description.