Add variable to disable homeserver url preview

This reverts commit 3387035400.

Enabling `jinja2_native` does help with the issue it is trying to
address - #151 (Github Pull Request), but it introduces a regression
when generating templates.

An example is
`roles/matrix-nginx-proxy/templates/nginx/conf.d/matrix-riot-web.conf.j2`,
which yields a strange resulting value of:

```
location /.well-known/acme-challenge {
    resolver 127.0.0.11 valid=5s;
    set $backend "matrix-certbot:8080";
    proxy_pass http://$backend;

    resolver 127.0.0.11 valid=5s;
    set $backend "matrix-certbot:8080";
    proxy_pass http://$backend;
}
```

For whatever reason (still to be investigated), the `if` block's
contents seem to have been outputted twice.

Reverting until this is resolved.
Until then, #151 would rely on the workaround and not on `jinja2_native`.

Fix value of nginx-proxy tmpfs size

Helps with #151 (Github Pull Request), but only for Ansible >= 2.7
and when Jinja >= 2.10 is in use.

For other version combinations we still need the workaround proposed
in the pull rqeuest.

Previously, we'd show an error like this:

{"changed": false, "item": null, "msg": "Detected an undefined required variable"}

.. which didn't mention the variable name
(`matrix_ssl_lets_encrypt_support_email`).

Looks like we may not have to do this,
since 1.4.2 fixes edge cases for people who used the broken
1.4.0 release.

We jumped straight to 1.4.1, so maybe we're okay.
Still, upgrading anyway, just in case.

Update mxisd (1.3.1 -> 1.4.1)

Remove hardcoded values in matrix-remove-all

Set Riot's enable_presence_by_hs_url to false if presence is disabled

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.

Fixed default url preview settings

make welcome.html customizable

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.

It's too many configuration options to keep them in a single list.
Trying to put some order.

add doc

Add some examples for caddy as an external webserver

Add additional room config options

- 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.

Make Dimension communicate to Synapse through Docker network

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

Putting a lot of comments inbetween `[matrix-servers]` and the example
host line may make someone decide to clean up the comment
and accidentally skip-over the `[matrix-servers]` part.

`{% 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).

Goofys Custom Endpoint Support

that's not how it works