Insert delta of current_state_events to be more efficient

Derive current_state_events from state groups

fix doc for purge_media_cache

purge_media_cache takes its arg from a query-param, not the POST body, for some
reason.

Make worker listener config backwards compat

Added username and password for turn server

It makes it possible to use a turn server that needs a username and
password instead of a token.

Update LruCache size estimate on clear

Allow configuring the Riot URL used in notification emails

Lowercase all email addresses before querying db

Since we store all emails in the DB in lowercase
(https://github.com/matrix-org/synapse/pull/1170)

Remove loading events logs

Lower the not retrying host log line to debug

Change resolve_state_groups call site logging to DEBUG

Measure metrics of string_cache

	Optimise state resolution

Get state at event rather than for room in push