improved initialization procedure

* process value doesn't retunr != 0 any more if some control flag was disabled
* check if we can set tuner at start, quit if now since otherwise we might run
  segfault.
* don't quit if we can't initialize the ADC, just disable the analog devices
  instead.
* fixed some error messages.
Fixed station search and load callbacks

* clear internal playlist upon starting, otherwise the playlist grows every
  time we start.
* decend search position hen no station can be found at requested pos.
* fixed debug print.