Feature request: PostgreSQL database support

[QuantumToasted]

As SourceMod has supported a PostgreSQL database driver since version 1.11.0.6666, it would be great if Sourcebans++ could also do the same, finally eliminating the need for certain server owners (such as myself) to need to maintain multiple, arguably redundant databases.

I tried to take it upon myself to implement support for it by simply modifying my local install, but I got hung up on this cryptic comment about FULLTEXT searches effectively stating that even if Database.php was properly configured to use pgsql instead of mysql, that something would fail due to what is effectively a MySQL-only feature being utilized/needed. I am not very familiar with FULLTEXT searches at all, but I was unable to find where this specific feature was actually utilized in SBPP. As PostgreSQL seems to have a suitable alternative, it might have been possible to get around this, but at the moment this is where I am stuck.

I would be more than happy to try my hand at a PR that would allow users to choose between PostgreSQL and MySQL/MariaDB during install time to prevent any hardcoded issues from cropping up, but any other MySQL-specific quirks that are used by SBPP would need to be pointed out to me.

Cheers!