ARI: Add channel technology agnostic out of call text messaging

ARI: Add channel technology agnostic out of call text messaging

This patch adds the ability to send and receive text messages from various
technology stacks in Asterisk through ARI. This includes chan_sip (sip),
res_pjsip_messaging (pjsip), and res_xmpp (xmpp). Messages are sent using the
endpoints resource, and can be sent directly through that resource, or to a
particular endpoint.

For example, the following would send the message "Hello there" to PJSIP
endpoint alice with a display URI of sip:asterisk@mycooldomain.org:

ari/endpoints/sendMessage?to=pjsip:alice&from=sip:asterisk@mycooldomain.org&body=Hello+There

This is equivalent to the following as well:

ari/endpoints/PJSIP/alice/sendMessage?from=sip:asterisk@mycooldomain.org&body=Hello+There

Both forms are available for message technologies that allow for arbitrary
destinations, such as chan_sip.

Inbound messages can now be received over ARI as well. An ARI application that
subscribes to endpoints will receive messages from those endpoints:

{
  "type": "TextMessageReceived",
  "timestamp": "2014-07-12T22:53:13.494-0500",
  "endpoint": {
    "technology": "PJSIP",
    "resource": "alice",
    "state": "online",
    "channel_ids": []
  },
  "message": {
    "from": "\"alice\" <sip:alice@127.0.0.1>",
    "to": "pjsip:asterisk@127.0.0.1",
    "body": "Watson, come here.",
    "variables": []
  },
  "application": "testsuite"
}

The above was made possible due to some rather major changes in the message
core. This includes (but is not limited to):
- Users of the message API can now register message handlers. A handler has
  two callbacks: one to determine if the handler has a destination for the
  message, and another to handle it.
- All dialplan functionality of handling a message was moved into a message
  handler provided by the message API.
- Messages can now have the technology/endpoint associated with them.
  Various other properties are also now more easily accessible.
- A number of ao2 containers that weren't really needed were replaced with
  vectors. Iteration over ao2_containers is expensive and pointless when
  the lifetime of things is well defined and the number of things is very
  small.

res_stasis now has a new file that makes up its structure, messaging. The
messaging functionality implements a message handler, and passes received
messages that match an interested endpoint over to the app for processing.

Note that inadvertently while testing this, I reproduced ASTERISK-23969.
res_pjsip_messaging was incorrectly parsing out the 'to' field, such that
arbitrary SIP URIs mangled the endpoint lookup. This patch includes the
fix for that as well.

Review: https://reviewboard.asterisk.org/r/3726

ASTERISK-23692 #close
Reported by: Matt Jordan

ASTERISK-23969 #close
Reported by: Andrew Nagy

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/12@420089 65c4cc65-6c06-0410-ace0-fbb531ad65f3