Largely refactor DSP tone detection routines.

Separate fax detection from digit detected.
Added CED (called) tone detection for fax (previously, only CNG (calling) was supported).
Separate DTMF/MF code paths where appropriate.
Allow detection of arbitary tones.

(closes issue #11796)
Reported by: dimas
Patches:
      v6-dsp-faxtones.patch uploaded by dimas (license 88)
Tested by: dimas, IgorG, Cache


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@103903 65c4cc65-6c06-0410-ace0-fbb531ad65f3