Save RTP audio to file: RTP Stream Analysis dialog allows save audio for non G.711...

Save RTP audio to file: RTP Stream Analysis dialog allows save audio for non G.711 codecs and mixed codecs

- spaghetti code for save was split into separate functions
- code saves G.711 only, all other codecs are saved as silence with correct duration
  - code is ready to include other codecs
  - code supports 8000 Hz sampling rate only, other rates are rejected with warning
  - bidirectional stream (forward and reverse) creates stereo .au file
- output is based on timestamps in RTP streams
  - save operation is slower than before because it is set of seek() - one per each codec sample
- code allows align of save audio:
  - as it is - each stream is saved from its beginning, no aling
  - to start of each other - later stream is prepended with silence
  - align saved audio to beginning of capture file - each stream is prepended with silence
- save to raw works correctly now - only payload is saved
  - old code was inserting G.711 silence time to time to raw data

Bug: 13242
Change-Id: I74d02a1cc1c75acf9ffe930d078c00a0555cbfb6
Reviewed-on: https://code.wireshark.org/review/19245
Petri-Dish: Anders Broman <a.broman58@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Anders Broman <a.broman58@gmail.com>