Add a welcome page to the static resources

Disable pager for ci script

... otherwise it hangs

This is largely a precursor for the removal of the bundled webclient. The idea
is to present a page at / which reassures people that something is working, and
to give them some links for next steps.

The welcome page lives at `/_matrix/static/`, so is enabled alongside the other
`static` resources (which, in practice, means the client API is enabled). We'll
redirect to it from `/` if we have nothing better to display there.

It would be nice to have a way to disable it (in the same way that you might
disable the nginx welcome page), but I can't really think of a good way to do
that without a load of ickiness.

It's based on the work done by @krombel for #2601.

Notes on upgrading to python3, and README updates.

Remove obsolete settings from docker homeserver.yaml

These aren't used, because we have a `log_config` setting.

Use labels to tag builds with their SHA1 version.

Replace mentions of Vector with Riot

This is useful for homeservers not intended for users, such as bot-only homeservers or ones that only process IoT data.

* Add note to UPGRADE.rst about removing riot.im from list of trusted identity servers

Signed-off-by: Aaron Raimist <aaron@raim.ist>

* Add changelog

Signed-off-by: Aaron Raimist <aaron@raim.ist>

This is a bit of a half-assed effort at fixing https://github.com/matrix-org/synapse/issues/4252. Fundamentally the right answer is to drop support for Python 2.

Drop sent_transactions

Fix removing pushers on python 3

Add a basic .editorconfig

This should fix some "Starting db connection from sentinel context" warnings,
and will mean we get metrics for these processes.

Signed-off-by: Aaron Raimist <aaron@raim.ist>

It turns out that we accept events with non-ascii IDs, which would later cause
an explosion during state res.

Fixes #4226

Signed-off-by: Aaron Raimist <aaron@raim.ist>

Signed-off-by: Aaron Raimist <aaron@raim.ist>

* Fix auto join failures for servers that require user consent

* Fix auto join failures for servers that require user consent

* fix transaction wrapping bug that caused get_user_id_by_threepid_txn to fail

* towncrier

* white space

* Clean up the CSS for the fallback login form

I was finding this hard to work with, so simplify a bunch of things. Each
flow is now a form inside a div of class login_flow.

The login_flow class now has a fixed width, as that looks much better than each
flow having a differnt width.

* Support m.login.sso

MSC1721 renames m.login.cas to m.login.sso. This implements the change
(retaining support for m.login.cas for older clients).

* changelog

* Add better diagnostics to flakey keyring test

* fix interpolation fail

* Check logcontexts before and after each test

* update changelog

* update changelog

* Some words about garbage collections and logcontexts

* Do a GC after each test to fix logcontext leaks

This feels like an awful hack, but...

* changelog

Ignore __pycache__ directories in schema delta dir