Fix matrix-synapse example for Caddy

Mautrix facebook

Docs for #161 (Github issue) and #168 (Github Pull Request).

Add option to proxy 3pid registration endpoints

Add registrations_require_3pid synapse option

Update URL for Matrix federation tester

The previous URL returns a 404.

Fix template indentation

Fix whitespace in templates

Use Jinja2 lstrip_blocks option in templates to ensure consistent
indentation in generated files.

This reverts commit 172d59ba05.

string before to_json when string value is expected

This prevents Ansible from sometimes failing to decrypt vault variables

Hopefully, we no longer lead people to believe that DNS SRV
records are going away forever and for all use-cases.

Fixes #156 (Github Issue)

Add the possibility to pass extra flags to the docker container

Add the ability to update user passwords with ansible

urlencode mxisd password

Update Synapse (0.99.3 -> 0.99.3.1)

As discussed in #151 (Github Pull Request), it's
a good idea to not selectively apply casting, but to do it in all
cases involving arithmetic operations.

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)