Clean up verify_json_objects_for_server

Conflicts:
	synapse/crypto/keyring.py

Add a couple more checks to the keyring

Fix a couple of bugs in the transaction and keyring code

Check if the user is banned when handling 3pid invites

Add `create_requester` function

Wrap the `Requester` constructor with a function which provides sensible
defaults, and use it throughout

Fix flake8 noise

Don't add rejections to the state_group, persist all rejections

Apparently flake8 v3 puts the error on a different line to v2. Easiest way to
make sure that happens is by putting the whole statement on one line :)

Apparently flake8 v3 doesn't like trailing comments on config settings.

Also remove the pep8 config, which didn't work (because it was missing W503)
and duplicated the flake8 config. We don't use pep8 on its own, so the config
was duplicative.

Implement updates and deletes for devices

Don't add rejected events if we've seen them befrore. Add some comments to explain what the code is doing mechanically

You can update the displayname of devices now.

Log the hostname the reCAPTCHA was completed on

Create index on user_ips in the background

Slightly saner logging for unittests

1. Give the handler used for logging in unit tests a formatter, so that the
output is slightly more meaningful

2. Log some synapse.storage stuff, because it's useful.

A bit of a cleanup for background_updates, and make sure that the real
background updates have run before we start the unit tests, so that they don't
interfere with the tests.

This could be useful information to have in the logs. Also comment about how & why we don't verify the hostname.