Add channel events for res_stasis apps

This change adds a framework in res_stasis for handling events from
channel topics. JSON event generation and validation code is created
from event documentation in rest-api/api-docs/events.json to assist in
JSON event generation, ensure consistency, and ensure that accurate
documentation is available for ALL events that are received by
res_stasis applications.

The userevent application has been refactored along with the code that
handles userevent channel blob events to pass the headers as key/value
pairs in the JSON blob. As a side-effect, app_userevent now handles
duplicate keys by overwriting the previous value.

Review: https://reviewboard.asterisk.org/r/2428/
(closes issue ASTERISK-21180)
Patch-By: Kinsey Moore <kmoore@digium.com>


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@388275 65c4cc65-6c06-0410-ace0-fbb531ad65f3

rest-api-templates/swagger_model.py

@@ -295,13 +295,17 @@ class Model(Stringify):
 
     def __init__(self):
         self.id = None
+        self.notes = None
+        self.description = None
         self.properties = None
 
     def load(self, id, model_json, processor, context):
         context = add_context(context, model_json, 'id')
+        # This arrangement is required by the Swagger API spec
         self.id = model_json.get('id')
         if id != self.id:
             raise SwaggerError("Model id doesn't match name", c)
+        self.description = model_json.get('description')
         props = model_json.get('properties').items() or []
         self.properties = [
             Property(k).load(j, processor, context) for (k, j) in props]