Discourse SSO (#560)

* Alter Discourse support to act as SSO provider.
Correct service group sync retry queueing.

* Correct default database enviroment variable names.

* Redirect to requested page after succesful login.

* Correct default redirect handling.
Correct attribute used to logout users on Discourse.
Improve logging messages to use parsed path on Discourse.

* Correct task retry syntax using bind=True.
Inherit from base exception so can catch TeamspeakErrors.

services/managers/util/ts3.py

@@ -249,7 +249,7 @@ class TS3Server(TS3Proto):
             self.send_command('use', keys={'sid': id})
 
 
-class TeamspeakError:
+class TeamspeakError(Exception):
     def __init__(self, code, msg=None):
         self.code = str(code)
         if not msg: