Ensure we never return a None event from _get_state_for_groups

Set request.authenticated_entity for application services

Re-enable receipts API.

Fix pending_calls metric to not lie

Add and use cached batched storage.get_state function.

Federation for end-to-end key requests.

Simplify LoginHander and AuthHandler

Add a few strategic new lines to break up the on_query_client_keys and on_claim_client_keys methods in federation_server.py

Dictionary and list caches

Add some metrics about the reactor