Create a separate module that tests whether the stream can be played

[GijsTimmers]

At the moment, there may be several reasons on why stream cannot be played:

• mplayer2 is not installed
• the stream is offline

These are currently being handled by Radio().afspelen(). I don't really like this.

Solution: create a separate class with modules that check whether everything is in place, e.g.

class CheckSetup():
    def stream():
        if stream_is_online:
            STREAM_ONLINE = True

    def mplayer(self):
        if mplayer_works:
            MPLAYER_WORKS = True
    def check(self)
        return(self.stream(), self.mplayer())

if not False in CheckSetup():
    continue