Swap self-hosted postgres for Amazon RDS.

This separates the app from the database -> good.

Sadly, there's no option for Amazon RDS to run postgres, so
where still stuck with MySQL. Oh well, made the migration easier at least.

Add mysql client libraries.
Update some salt/infrastructure documnentation.
Make sure www owns the slingsby logs.

This is needed because it seems that in some cases,
the log file would be owned by root, and thus slingsby running as
www would not be able to write to it, and fail over.
Remove archive.Video for now.

Can probably be added back once we have an actual implementation for it.
Remove old.ntnui.no authentication.

This enables us to open up the auth module, which no longer contains any
badly implemented crypto stuff.

Also fixes some smaller issues in a couple of modules, adding logging to
file on errors, etc.