RadioManager:
add_station()
remove_station()
get_station()

RadioStation:
get_tree()
load_lists()

RadioList:
get_items()

RadioItem:
get_playlist()


example hierarchy:

RadioManager
    RadioStation (shoutcast)
        RadioList (rock)
            RadioItem
            RadioItem
        RadioList (80s)
            RadioItem
            RadioItem
    RadioStation (last.fm)
        RadioItem (personal)
        RadioItem (recommended)
    RadioStation (podcasts)
        RadioList (some random podcast)
            RadioItem
            RadioItem