SYN-208/SYN-228: Add runtime checks on startup to enforce that JPEG/PNG support is included when installing pillow.

Look for name, topic in the event content rather than the event itself when persisting room name and topic events

Supply auth_chain along with current state in '/state/', fetch auth events from a remote server if we are missing some of them

Replace distributor deferred list, with a simple for loop until I understand why the former breaks and the latter doesn't

Add gotcha: The content repository requires additional cygwin packages.

Add windows (cygwin) install instructions.

Conflicts:
	synapse/state.py