Fixes #230 (Github Issue).

Related to https://github.com/Half-Shot/matrix-appservice-discord/issues/510

It adds support for a new `DISABLE_SENDER_VERIFICATION` environment
variable that can be used to disable verification of sender addresses.

It doesn't matter for us, but we upgrade to keep up with latest.

Fix apt message: docker doesn't support arch 'i386'

Related to #223 (Github Pull Request)

Update synapse (1.1.0 -> 1.2.0)

Update nginx (1.17.1 -> 1.17.2)

Upgrade riot-web (1.2.4 - 1.3.0)

introduce configuration to change riot branding / title

Looks like these client ids are actually integers,
but unless we pass them as a string, the bridge would complain with
an error like:

    {"field":"data.auth.clientID","message":"is the wrong type","value":123456789012345678,"type":"string","schemaPath":["properties","auth","properties","clientID"]}

Explicitly-casting to a string should fix the problem.

The Discord bridge should probably be improved to handle both ints and
strings though.

Fixes #216 (Github Issue).

Update to riot 1.2.3

We do restart Synapse explicitly, but some other services
(bridges, matrix-corporal, ..) may not restart sometimes.

It's best to restart all services explicitly.

Regression since 174a6fcd1b3, #204 (Github Pull Request),
which only affects new servers.

Old servers which had their passkey.pem file relocated were okay.

Bump nginx version to 1.17.1

ef5e4ad061 intentionally makes us conform to
the logging format suggested by the official Docker image.

Reverting this part, because it's uglier.

This likely should be fixed upstream as well though.

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.

Fixes a regression introduced during the upgrade to
Synapse v1.1.0 (in 2b3865ceea).

Since Synapse v1.1.0 upgraded to Python 3.7
(https://github.com/matrix-org/synapse/pull/5546),
we need to use a different modules directory when mounting
password provider modules.

Fixes a problem introduced by da6edc9cba.

Related to #145 (Github Pull Request).

This is a new feature of Synapse v1.1.0.

Discussed in #145 (Github Pull Request).

Make Discord bridge configuration playbook-managed