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.

Split out static auth methods from Auth object

Change device_inbox stream index to include user

Restore default bind address

Fix formatting blooper introduced in https://github.com/matrix-org/synapse/pull/1672 :/

Fix spurious Unhandled Error log lines