Remove riot.im from list of trusted identity servers

This brings the list in line with the new default as of https://github.com/matrix-org/synapse/pull/4207

Fix well known self check

Allow Synapse log levels to be configured (#23)

Add initial version of maintenance and troubleshooting doc

Link to the restoring media store guide

It isn't below anymore

Updated "Controlling Matrix federation" link

Missing file ending results in 404

Allow a few parts of Riot config.json to be configured (#24)

Disable TLS 1.0

This also raises the default from 5 seconds to 15 seconds.

Regression since 3fd6fd647f

Allow specifying which parts of the role run from playbooks

Pretty much all variables live in their own `matrix_<whatever>`
prefix now and are grouped closer together in the default
variables file (`roles/matrix-server/defaults/main.yml`).

Update riot-web (0.17.0 -> 0.17.3)

It should be `/bin/mkdir` and `/bin/chown` on Ubuntu 18.04 for example.
Still, it doesn't seem like we need to create and chown these
directories at all, since the playbook takes care of creating them
and setting appropriate permission by itself.

Mautrix whatsapp

Regression since 67a445a74a

It's been incorrect since 23e4a473