Fixes #562 (Github Issue)

Fixes #586 (Github Issue)

Related to #557 (Github Pull Request).

Related to #540 (Github Pull Request).

Related to #551 and #555 (Github Pull Requests).

We can undo this once https://github.com/ma1uta/ma1sd/issues/44 gets
resolved.

Note the potential breaking change

Resolves #474

Related to #454 (Github Pull Request).

Related to #436 (Github Pull Request).

Related to #425 (Github Pull Request).

Related to #386 (Github Pull Request)

Related to #339 (Github Pull Request).

Prompted by: https://matrix.org/blog/2019/11/09/avoiding-unwelcome-visitors-on-private-matrix-servers

This is a bit controversial, because.. the Synapse default remains open,
while the general advice (as per the blog post) is to make it more private.

I'm not sure exactly what kind of server people set up and whether they
want to make the room directory public. Our general goal is to favor
privacy and security when running personal (family & friends) and corporate
homeservers, both of which likely benefit from having a more secure default.

Fixes #255 (Github Issue).

Fixes #71 (Github Issue).

Also discussed previously in #213 (Github Pull Request).

shared-secret-auth and rest-auth logging is still at `INFO`
intentionally, as user login events seem more important to keep.
Those modules typically don't spam as much.

Somewhat related to #213 (Github Pull Request).

We've been moving in the opposite direction for quite a long time.
All services should just leave logging to systemd's journald.

Well, `config.yaml` has been playbook-managed for a long time.
It's now extended to match the default sample config of the Discord
bridge.

With this patch, we also make `registration.yaml` playbook-managed,
which leads us to consistency with all other bridges.

Along with that, we introduce `./config` and `./data` separation,
like we do for the other bridges.

- changelog entry for commit 4797469383