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

Split out static state methods from StateHandler

Optionally measure size of cache by sum of length of values

Instead of calculating the size of the cache repeatedly, which can take
a long time now that it can use a callback, instead cache the size and
update that on insertion and deletion.

This requires changing the cache descriptors to have two caches, one for
pending deferreds and the other for the actual values. There's no reason
to evict from the pending deferreds as they won't take up any more
memory.