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).

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)

Doing this for consistency.

Related to #117 (Github Pull Request).

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.

Related to #105 (Github Pull Request).

Generates the link required to add the Bridge to a Discord server.

Bridge is setup to work on the matrix side with this, but the discord invite link is not automatically generated.

Fixes #69 (Github Issue)

Using `docker_container` with a `cap_drop` argument requires
Ansible >=2.7.

We want to support older versions too (2.4), so we either need to
stop invoking it with `cap_drop` (insecure), or just stop using
the module altogether.

Since it was suffering from other bugs too (not deleting containers
on failure), we've decided to remove `docker_container` usage completely.

It's not important for us, as it only contains
some ACME-related fix.

`matrix_synapse_no_tls` is now implicit, so we've gotten rid of it.

The `homeserver.yaml.j2` template has been synchronized with the
configuration generated by Synapse v0.99.1 (some new options
are present, etc.)

This reverts commit 536c85619f.

Looks like binding metrics on IPv6 (`::`) fails with an error:

socket.gaierror: [Errno -2] Name does not resolve

For consistency with all our other listeners,
we make this one bind on the `::` address too
(both IPv4 and IPv6).

Additional details are in #91 (Github Pull Request).

Docker apparently doesn't like IPv6.

This reverts commit 0dac5ea508.

Relying on pyOpenSSL is the Ansible way of doing things, but is
impractical and annoying for users.

`openssl` is easily available on most servers, even by default.
We'd better use that.