Add 8.33 kHz support to the commradio

Add 8.33 kHz support to the commradio

Usage:
Add
  <comm-radio>
    <name>comm</name>
    <number>0</number>
    <eight-point-three type="bool">true</eight-point-three>
  </comm-radio>
to the instrumentation.xml

If eight-point-three is disabled nor not present, previous functionality is unchanged

If eight-point-three is enabled,
set
/instrumentation/comm[x]/frequencies/[selected|standby]-mhz
to the desired 8.33 channel (118.000..136.990) or
/instrumentation/comm[x]/frequencies/[selected|standby]-channel
to the desired channel-number (0..3039).

Valid channels are:
xxx.000
xxx.005
xxx.010
xxx.015
xxx.025
xxx.030
xxx.035
xxx.040
xxx.050
xxx.055
xxx.060
xxx.065
xxx.075
xxx.080
xxx.085
xxx.090
where 118.0 <= xxx <= 136.990