Use common path for systemctl in lets encrypt cron

Update homeserver.yaml with some new options we could enable

Doing this for consistency.

Related to #117 (Github Pull Request).

Allow configuring push content for matrix-synapse

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.

Federation self-check respects matrix_synapse_federation_enabled

`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.

Start appservice-irc as non-root

Add option to enable Dimension widgets serve sites with self signed certs

Fix Matrix homeserver name in Dimension configuration

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`.

Fix Dimension documentation

Related to #107 and #111 (Github Pull Requests)

Provide Dimension documentation

Implement self-hosted Dimension server

Related to #108 (Github Pull Request).

Fix indenting of generators value

allow exposing mautrix_telegram port

Upgrade riot-web to v1.0.3