Make roles more independent of one another

With this change, the following roles are now only dependent
on the minimal `matrix-base` role:
- `matrix-corporal`
- `matrix-coturn`
- `matrix-mailer`
- `matrix-mxisd`
- `matrix-postgres`
- `matrix-riot-web`
- `matrix-synapse`

The `matrix-nginx-proxy` role still does too much and remains
dependent on the others.

Wiring up the various (now-independent) roles happens
via a glue variables file (`group_vars/matrix-servers`).
It's triggered for all hosts in the `matrix-servers` group.

According to Ansible's rules of priority, we have the following
chain of inclusion/overriding now:
- role defaults (mostly empty or good for independent usage)
- playbook glue variables (`group_vars/matrix-servers`)
- inventory host variables (`inventory/host_vars/matrix.<your-domain>`)

All roles default to enabling their main component
(e.g. `matrix_mxisd_enabled: true`, `matrix_riot_web_enabled: true`).
Reasoning: if a role is included in a playbook (especially separately,
in another playbook), it should "work" by default.

Our playbook disables some of those if they are not generally useful
(e.g. `matrix_corporal_enabled: false`).

roles/matrix-riot-web/defaults/main.yml

@@ -1,13 +1,17 @@
-# By default, this playbook installs the Riot.IM web UI on the `hostname_riot` domain.
-# If you wish to connect to your Matrix server by other means,
-# you may wish to disable this.
 matrix_riot_web_enabled: true
 
 matrix_riot_web_docker_image: "bubuntux/riot-web:v0.17.8"
 
 matrix_riot_web_data_path: "{{ matrix_base_data_path }}/riot-web"
 
+matrix_riot_web_container_expose_port: false
+
+# List of systemd services that matrix-riot-web.service depends on
+matrix_riot_web_systemd_required_services_list: ['docker.service']
+
 # Riot config.json customizations
+matrix_riot_web_default_hs_url: ""
+matrix_riot_web_default_is_url: ~
 matrix_riot_web_disable_custom_urls: true
 matrix_riot_web_disable_guests: true
 matrix_riot_web_integrations_ui_url: "https://scalar.vector.im/"
@@ -18,7 +22,6 @@ matrix_riot_web_integrations_jitsi_widget_url: "https://scalar.vector.im/api/wid
 matrix_riot_web_roomdir_servers: ['matrix.org']
 matrix_riot_web_welcome_user_id: "@riot-bot:matrix.org"
 
-
 # Riot home.html customizations
 # Default home.html template file
 matrix_riot_web_homepage_template: "{{ role_path }}/templates/home.html.j2"