Makes Nginx configuration optional

[conorsch]

The role provides the sane default of a preconfigured Nginx vhost, created following the Jitsi Meet project docs. That's fine for a baseline configuration, but makes managing for the Jitsi service via a separate role quite difficult. Let's make the Nginx configuration opt-out, so it still runs by default but can be skipped if admins prefer another method for managing vhosts.

The vhost template still ships with the role and should be consulted when writing a custom vhost config.

Closes #28.

[msheiny]

I have broughteth my stamp made from the finest rubber trees in the land. BE GONE PR!!!!!