improve readability

(adapting strings and URLs)

This matches the way the ports are written in prerequisites.md and is the format that UFW likes.

* clarify the config path

added path to the correct vars.yaml in matrix-synapse

* Fix configuration path

Co-authored-by: Slavi Pantaleev <slavi@devture.com>

We do this for 2 reasons:

- so we can control things which are not controllable using environment
variables (for example `stunServers` in jitsi/web, since we don't wish
to use the hardcoded Google STUN servers if our own Coturn is enabled)

- so playbook variable changes will properly rebuild the configuration.
When using Jitsi environment variables, the configuration is only built
once (the first time) and never rebuilt again. This is not the
consistent with the rest of the playbook and with how Ansible operates.
We're not perfect at it (yet), because we still let the Jitsi containers
generate some files on their own, but we are closer and it should be
good enough for most things.

Related to #415 (Github Pull Request).

Discussed in #412 (Github Issue).

I am new to synapse. Thanks so much for these playbooks!

I wasn't sure how you actual activate dimensions after setting these variables. Should you re run 

ansible-playbook -i inventory/hosts setup.yml --tags=setup-all
ansible-playbook -i inventory/hosts setup.yml --tags=start

? If so perhaps you could tell the readers to do this somewhere in the help file

Thanks =]

Fixes #396 (Github Issue).

Added steps to configure appservice webhooks in the dimension manager.

This fixes an incorrect indentation in the database specification for
appservice-irc which caused matrix-appservice-irc to refuse to start
with the remarkably unhelpful error message:

```
ERROR:CLI Failed to run bridge.
```

This also updates doc links to the new matrixdotorg repo because the
tedomum repo contains out-of-date documentation.