Adds new formats to app_alarmreceiver, ALAW calls support and enhanced protection.

Commiting this on behalf of Kaloyan Kovachev (license 5506).
AlarmReceiver now supports the following DTMF signaling types:
 - ContactId
 - 4x1
 - 4x2
 - High Speed
 - Super Fast
We are also auto-detecting which signaling is being received. So support for
those protocols should work out-the-box. Correctly identify ALAW / ULAW calls.
Some enhanced protection for broken panels and malicious callers where added.

(closes issue ASTERISK-20289)
Reported by: Kaloyan Kovachev

Review: https://reviewboard.asterisk.org/r/2088/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@375150 65c4cc65-6c06-0410-ace0-fbb531ad65f3