OneTouchRecord: Make so Monitor/MixMonitor can be toggled/started/stopped.

The OneTouchRecord feature has historically been a toggle.  This patch
adds the ability to make the OneTouchRecord hook optionally start/stop
recording only.  If OneTouchRecord is already doing what is requested then
only the invoker hears the courtesy tone and/or start/stop recording
message.

The new feature is written so we could easily add explicit start/stop
recording DTMF hooks for Monitor and MixMonitor.

The majority of the changes in bridge_builtin_features.c is a refactoring
of the OneTouchRecord code (Monitor and MixMonitor versions) so it is easy
to direct the toggle/start/stop functionality.

Review: https://reviewboard.asterisk.org/r/2655/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@393612 65c4cc65-6c06-0410-ace0-fbb531ad65f3