Add queue member paused hints

This patch adds the ability in Queue to raise a hint when a member's paused
state changes. The hint uses the form 'Queue:{queue_name}_pause_{member_name}',
where {queue_name} and {member_name} are the name of the queue and the name
of the member to subscribe to, respectively.

For example: exten => 8501,hint,Queue:sales_pause_mark.

Members will show as In Use when paused.

Note that the format of the queue pause hint was changed slightly from what
is on the issue to accomodate suggestion on the code review.

Review: https://reviewboard.asterisk.org/r/2254

(closes issue ASTERISK-20842)
Reported by: Philippe Lindheimer
patches:
  qpause-10-378206.diff uploaded by Philippe Lindheimer (license 5519)
  qpause-11-378206.diff uploaded by Philippe Lindheimer (license 5519)
  qpause-trunk-378206.diff uploaded by Philippe Lindheimer (license 5519)



git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@396010 f38db490-d61c-443f-a65b-d21fe96a405b