Change from / reply-to for feedback form

Also merge Joomla helper into external users file.

We cannot get the id/username from the display name, so we have to
display usernames instead.

If the email address user inputed has forced SPF check, the email will not be received by major ESPs.

Include link to documentation website

Also use $definitions variable in queries.

And now we have local Joomla integration, we don't have to fail if the Joomla plugin isn't installed.

Added local Joomla integration rather than relying on Joomla having the separate plugin installed. (But still support the plugin if it's there, as it gives a lot more flexibility)

For logged-out users only.