res_stasis: Extend bridge type to be a comma separated list of bridge attributes.

This change turns the bridge type field into a comma separated list of attributes.
These attributes include: mixing, holding, dtmf_events, and proxy_media. By setting
the various attributes a user can control the type of bridge created with the
behavior they need for their application.

(closes issue ASTERISK-23437)
Reported by: Matt Jordan

Review: https://reviewboard.asterisk.org/r/3359/
........

Merged revisions 410904 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@410905 65c4cc65-6c06-0410-ace0-fbb531ad65f3

CHANGES

@@ -103,6 +103,16 @@ Core
  * Exposed sorcery-based configuration files like pjsip.conf to dialplans via
    the new AST_SORCERY diaplan function.
 
+=======
+ARI
+------------------
+ * The live recording object on recording events now contains a target_uri
+   field which contains the URI of what is being recorded.
+
+ * The bridge type used when creating a bridge is now a comma separated list of
+   bridge properties. Valid options are: mixing, holding, dtmf_events, and
+   proxy_media.
+
  * A channelId can now be provided when creating a channel, either in the
    uri (POST channels/my-channel-id) or as query parameter.  A local channel
    will suffix the second channel id with ';2' unless provided as query