Add unknown user ID check. Use store.get_aliases_for_room(room_id) when searching for services by alias.

Previously, this would only return the HTTP body as JSON, and discard other
response information (e.g. the HTTP response code). This has now been changed
to throw a CodeMessageException on a non-2xx response, with the response code
and body, which can then be parsed as JSON.

Affected modules include:
 - Registration/Login (when using an email for IS auth)

Implement restricted namespace checks. Begin fleshing out the main hook for notifying application services.

Expose handler.get_services_for_event which manages the checks for all
services.

Add a media/v1/identicon resource for generating identicons

Conflicts:
	synapse/handlers/__init__.py
	synapse/storage/__init__.py

Conflicts:
	README.rst
	setup.py

Hotfixes v0.6.1d

Conflicts:
	README.rst