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).

Add Slack bridging support

Add mautrix-hangouts bridge role and documentation

Describe setting up SMTP server with Sendgrid

Update synapse (1.3.0 -> 1.3.1) and riot-web (1.3.2 -> 1.3.3)

Thanks to @ralfi!

Contributed by @ralfi.

missing Map /.well-known/matrix/server for server discovery

Continuation of #246 (Github Pull Request)

Update synapse (1.2.1 -> 1.3.0)