app_queue: Add RealTime support for queue rules

This patch gives the optional ability to keep queue rules in RealTime. It is
important to note that with this patch:
 (a) Queue rules in RealTime are only examined on module load/reload
 (b) Queue rules are loaded both from the queuerules.conf file as well as the
     RealTime backend
To inform app_queue to examine RealTime for queue rules, a new setting has been
added to queuerules.conf's general section "realtime_rules". RealTime queue
rules will only be used when this setting is set to "yes".

The schema for the database table supports a rule_name, time, min_penalty, and
max_penalty columns. min_penalty and max_penalty can be relative, if a '-' or
'+' literal is provided. Otherwise, the penalties are treated as constants.

For example:
rule_name, time, min_penalty, max_penalty
'default', '10', '20', '30'
'test2', '20', '30', '55'
'test2', '25', '-11', '+1111'
'test2', '400', '112', '333'
'test3', '0', '4564', '46546'
'test_rule', '40', '15', '50'

which would result in :

Rule: default
 - After 10 seconds, adjust QUEUE_MAX_PENALTY to 30 and adjust
   QUEUE_MIN_PENALTY to 20
Rule: test2
 - After 20 seconds, adjust QUEUE_MAX_PENALTY to 55 and adjust
   QUEUE_MIN_PENALTY to 30
 - After 25 seconds, adjust QUEUE_MAX_PENALTY by 1111 and adjust
   QUEUE_MIN_PENALTY by -11
 - After 400 seconds, adjust QUEUE_MAX_PENALTY to 333 and adjust
   QUEUE_MIN_PENALTY to 112
Rule: test3
 - After 0 seconds, adjust QUEUE_MAX_PENALTY to 46546 and adjust
   QUEUE_MIN_PENALTY to 4564
Rule: test_rule
 - After 40 seconds, adjust QUEUE_MAX_PENALTY to 50 and adjust
   QUEUE_MIN_PENALTY to 15

If you use RealTime, the queue rules will be always reloaded on a module
reload, even if the underlying file did not change. With the option disabled,
the rules will only be reloaded if the file was modified.

Review: https://reviewboard.asterisk.org/r/3607/

ASTERISK-23823 #close
Reported by: Michael K
patches:
  app_queue.c_realtime_trunk.patch uploaded by Michael K (License 6621)
........

Merged revisions 420624 from http://svn.asterisk.org/svn/asterisk/branches/13


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@420625 65c4cc65-6c06-0410-ace0-fbb531ad65f3