v0.50.POWER.1 - dot-nginx.conf reversal

This release reverts 1 feature (sort of)

• The "dot-nginx.conf" feature has been reverted. This is due to two reasons:
• • The architecture of the system was faulty to the point where we delegated to the user things that should have been delegated to the machine. This meant that, for example, public certificate paths had to be updated manually.
• • Moreover, the "vanilla" Mail-in-a-Box already has a similar system (even though it's very poorly or not documented at all), on which we will fall back on.
• • • Custom nginx directives for a domain example.com are stored in /home/user-data/www/example.com.conf - the difference between MiaB and Power-MiaB is that this file will always exist.
• • We still keep the changes that make it so that the Webmail (on the /mail path) will now be served on the primary directory only.

Other changes

• Nextcloud was updated to version 19.0.3
• Admin panel: Bootstrap was updated to version 4.5.2