[onkyo] Add support for Favourited Radio Stations

[Cossey]

With the changes I added earlier this year to the Input Selector drop down displaying custom labels; the next thing to add is the ability to display the saved Radio stations in another drop down list with the radio station frequency number and possibly a name if that gets recorded from RDS.

This data is pulled from the same xml file that contains the Input labels and should be processed at the same time as the Input labels.