ARI: Add subscription support

This patch adds an /applications API to ARI, allowing explicit management of
Stasis applications.

 * GET /applications - list current applications
 * GET /applications/{applicationName} - get details of a specific application
 * POST /applications/{applicationName}/subscription - explicitly subscribe to
   a channel, bridge or endpoint
 * DELETE /applications/{applicationName}/subscription - explicitly unsubscribe
   from a channel, bridge or endpoint

Subscriptions work by a reference counting mechanism: if you subscript to an
event source X number of times, you must unsubscribe X number of times to stop
receiveing events for that event source.

Review: https://reviewboard.asterisk.org/r/2862

(issue ASTERISK-22451)
Reported by: Matt Jordan
........

Merged revisions 400522 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@400523 65c4cc65-6c06-0410-ace0-fbb531ad65f3

include/asterisk/endpoints.h

@@ -76,6 +76,19 @@ const char *ast_endpoint_state_to_string(enum ast_endpoint_state state);
  */
 struct ast_endpoint;
 
+/*!
+ * \brief Finds the endpoint with the given tech/resource id.
+ *
+ * Endpoints are refcounted, so ao2_cleanup() when you're done.
+ *
+ * \param id Tech/resource id to look for.
+ * \return Associated endpoint.
+ * \return \c NULL if not found.
+ *
+ * \since 12
+ */
+struct ast_endpoint *ast_endpoint_find_by_id(const char *id);
+
 /*!
  * \brief Create an endpoint struct.
  *
@@ -125,6 +138,18 @@ const char *ast_endpoint_get_tech(const struct ast_endpoint *endpoint);
  */
 const char *ast_endpoint_get_resource(const struct ast_endpoint *endpoint);
 
+/*!
+ * \brief Gets the tech/resource id of the given endpoint.
+ *
+ * This is unique across all endpoints, and immutable.
+ *
+ * \param endpoint The endpoint.
+ * \return Tech/resource id of the endpoint.
+ * \return \c NULL if endpoint is \c NULL.
+ * \since 12
+ */
+const char *ast_endpoint_get_id(const struct ast_endpoint *endpoint);
+
 /*!
  * \brief Updates the state of the given endpoint.
  *