Bump riot web version 1.3.6 -> 1.4.0

Upgrade Synapse (1.3.1 -> 1.4.0)

Update certbot (0.37.1 -> 0.38.0)

Update nginx (1.17.3 -> 1.17.4)

Update configuring-well-known.md

Attempt at fixing #268 (Github Issue)

Update riot-web (1.3.5 -> 1.3.6)

Disable docker network tasks in check mode to allow running the playbook in check mode (--check --diff)

Upgrade riot-web (1.3.3 -> 1.3.5)

Fixes #255 (Github Issue).

Fixes #257 (Github Issue)

Move pipelining configuration to ansible.cfg

More Apache ProxyPass directives need 'nocanon'

Invitations weren't working for me until I added 'nocanon' to these additional places. Until then, invitations failed with "Invalid signature for server ..." errors, as in https://github.com/matrix-org/synapse/issues/3294 .

I didn't check whether the user_directory/search proxy line also needs it, I just assumed it should have it too.

The other two proxy lines in this example also include a 'retry=0' parameter. That's a separate issue; I haven't touched it here.

Fix force-pulling of mautrix-whatsapp

Add haproxy doc

Fixes #70 (Github Issue).

Fixes #71 (Github Issue).