automatic channel retune

[rocus]

It is the intention of this change that If you are using welle-cli with the webinterface you can choose any radiostation (as scanned bij welle.io) by means of an adapted m3u file. If a channel change is needed it will be done automatically. Because such a channel change takes some time your streamer will problably time out. Wait some seconds (untill after the channel change is completed , normally 10 seconds) and choose the radiostation again. In the m3u file for a specific radiostation the required channel is incorporated. You can craft such an m3u file with two helper files (in the root directory of this repository). You can also made them by hand by looking at the normal browser-webinterface of welle-cli. "old" m3u files still work but don't initiate a channel change.

The webinterface in a browser stll works as it used to be: you see only the radiostations of the currently chosen channel and you can change the channel by hand.

There are only a few changes in the file WebRadioInterface.cpp. Because I am not an experienced c++ programmer, maybe you can improve on some changes!

This is also my first attempt to use git and github so please be gentle!