- don't read the channel always from tacan[0] (even if the existence of

- don't read the channel always from tacan[0] (even if the existence of
  a second tacan may not be likely)
- remove some dead code
- simplify <name>/<number> handling
- let a listener watch over input props and search for new channel/frequency
- allow to set channel number as one number (rather than as single digits),
  as some aircraft may prefer this (the ch53 does so); this is to be set
  in /instrumentation/tacan[n]/frequencies/selected-channel[0]