webaccess: started to implement input/output device selection
webaccess: fixed widgets broken command send

Added audio devices IO configuration table
Use first found channel of its type (pan/tilt/master intensity/red/green/...).

Former code used last found channel -- when there were two PAN coarse channels,
then the latter was used. In case the fixture author forgot to set LSB/MSB bytes,
the LSB (fine) channel was used since it is (almost?) always after MSB (coarse) channel.
This change makes QLC+ use the first one.