New configuration variable RAW_AUDIO_UDP_DEST

A new configuration variable for local receivers have been added,
RAW_AUDIO_UDP_DEST, which makes it possible to stream the raw audio read
by SvxLink from the audio device to a UDP port. This feature was mainly
added for debugging but may be usable for other things as well.
Merged the devcal branch into develop

The devcal branch has been used to develop a new calibration utility,
devcal. This utility can be used to calibrate all receivers and
transmitters in the system so that all levels are the same. The default
calibration is done so that max deviation of the channel, e.g. 5kHz, is
-6dBF (half way from maximum AD/DA value). This leaves some headroom for
overdeviation without distorsion in the digital domain.

While implementing this the following also changed:

* New TX config variable: MASTER_GAIN. Use this configuration variable
  to adjust the gain for a transmitter if the slider cannot be pushed
  high enough in the audio mixer or to fine tune during calibration.

* Fractionals can now be used in the PREAMP config var. It was not
  enough with integer resolution to achieve exact calibration.
FM demodulator improvements

* Bugfixes
* Improvements to make deviation measurements more exact
Receiver deviation calibration improvements

* Now applying a flat top window before the Goertzel to make the
  amplitude measurements more accurate when the tone being measured is
  not spot on the frequency or the tone period length does not match the
  Goertzel block length.

* The Goertzel bandwidth was widened from 10 to 20 Hz to better handle
  inexact calibration frequency.

* Printing deviation four tims per second instead of ten.

* Forcing DTMF_MUTING to off so that it will not interfere with the
  measurements if using DTMF for calibration.