Use matrix_docker_network and matrix_base_data_path in matrix-remove-all
instead of hardcoded default values.

Use an int conversion in the computation of the value of
matrix_nginx_proxy_tmp_directory_size_mb, to have the integer value
multiplied by 50 instead of having the string repeated 50 times.

It doesn't hurt to attempt renewal more frequently, as it only does
real work if it's actually necessary.

Reloading, we postpone some more, because certbot adds some random delay
(between 1 and 8 * 60 seconds) when renewing. We want to ensure
we reload at least 8 minutes later, which wasn't the case.

To make it even safer (in case future certbot versions use a longer
delay), we reload a whole hour later. We're in no rush to start using
the new certificates anyway, especially given that we attempt renewal
often.

Somewhat fixes #146 (Github Issue)

The code used to check for a `homeserver.yaml` file and generate
a configuration (+ key) only if such a configuration file didn't exist.

Certain rare cases (setting up with one server name and then
changing to another) lead to `homeserver.yaml` being there,
but a `matrix.DOMAIN.signing.key` file missing (because the domain
changed).
A new signing key file would never get generated, because `homeserver.yaml`'s
existence used to be (incorrectly) satisfactory for us.

From now on, we don't mix things up like that.
We don't care about `homeserver.yaml` anymore, but rather
about the actual signing key.

The rest of the configuration (`homeserver.yaml` and
`matrix.DOMAIN.log.config`) is rebuilt by us in any case, so whether
it exists or not is irrelevant and doesn't need checking.

- matrix_enable_room_list_search - Controls whether searching the public room list is enabled.
 - matrix_alias_creation_rules - Controls who's allowed to create aliases on this server.
 - matrix_room_list_publication_rules - Controls who can publish and which rooms can be published in the public room list.

Media is pulled from client side, so we specify external Matrix DNS name as mediaUrl

`{% matrix_s3_media_store_custom_endpoint_enabled %}` should have
been `{% if matrix_s3_media_store_custom_endpoint_enabled %}` instead.

Related to #132 (Github Pull Request).

that's not how it works

This (should) check if custom endpoint is enabled.

Creates the configuration variable to toggle custom endpoint and the default custom endpoint.

In most cases, there's not really a need to touch the system
firewall, as Docker manages iptables by itself
(see https://docs.docker.com/network/iptables/).

All ports exposed by Docker containers are automatically whitelisted
in iptables and wired to the correct container.

This made installing firewalld and whitelisting ports pointless,
as far as this playbook's services are concerned.

People that wish to install firewalld (for other reasons), can do so
manually from now on.

This is inspired by and fixes #97 (Github Issue).

Fixes #129 (Github Issue).

Unfortunately, we rely on `service_facts`, which is only available
in Ansible >= 2.5.

There's little reason to stick to an old version such as Ansible 2.4:
- some time has passed since we've raised version requirements - it's
time to move into the future (a little bit)
- we've recently (in 82b4640072) improved the way one can run
Ansible in a Docker container

From now on, Ansible >= 2.5 is required.

By default, `--tags=self-check` no longer validates certificates
when `matrix_ssl_retrieval_method` is set to `self-signed`.

Besides this default, people can also enable/disable validation using the
individual role variables manually.

Fixes #124 (Github Issue)

Most (all?) of our Matrix services are running in the `matrix` network,
so they were safe -- not accessible from Coturn to begin with.

Isolating Coturn into its own network is a security improvement
for people who were starting other services in the default
Docker network. Those services were potentially reachable over the
private Docker network from Coturn.

Discussed in #120 (Github Pull Request)

This is more explicit than hiding it in the role defaults.

People who reuse the roles in their own playbook (and not only) may
incorrectly define `ansible_host` to be a hostname or some local address.

Making it more explicit is more likely to prevent such mistakes.

Doing this for consistency.

Related to #117 (Github Pull Request).

Currently the nginx reload cron fails on Debian 9 because the path to
systemctl is /bin/systemctl rather than /usr/bin/systemctl.

CentOS 7 places systemctl in both /bin and /usr/bin, so we can just use
/bin/systemctl as the full path.

This allows overriding the default value for `include_content`. Setting
this to false allows homeserver admins to ensure that message content
isn't sent in the clear through third party servers.

`matrix_nginx_proxy_data_path` has always served as a base path,
so we're renaming it to reflect that.

Along with this, we're also introducing a new "data path" variable
(`matrix_nginx_proxy_data_path`), which is really a data path this time.
It's used for storing additional, non-configuration, files related to
matrix-nginx-proxy.

It's been reported that YAML parsing errors
would occur on certain Ansible/Python combinations for some reason.

It appears that a bare `{{ matrix_dimension_admins }}` would sometimes
yield things like `[u'@user:domain.com', ..]` (note the `u` string prefix).

To prevent such problems, we now explicitly serialize with `|to_json`.