InitialSync: load the 30 last messages of each room so that a full page of messages can be displayed without additionnal request

Use event age to recognise which calls are current and which aren't and hence support answering calls that were placed before we loaded the page.

Comment out password reset for now, until the mechanism is fully discussed (IS token auth vs HS auth)

Added support for the HS to send emails. Use it to send password resets. Added email_smtp_server and email_from_address config args. Added emailutils.

Fix bug where we incorrectly calculated 'age_ts' from 'age' key rather than the reverse. Don't transmit age_ts to clients for now.

Merge branch 'develop' of github.com:matrix-org/synapse into registration-api-changes in preparation for re-merge to develop.

Define a CLOS-like 'around' modifier as a decorator, to neaten up the 'orig_*' noise of wrapping the setUp()/tearDown() methods