Purge purge purge

There are several tables in the DB that we keep feeding with new data but never purge.

This makes the DB slower and also leads to failures (transaction timeouts or lock wait timeouts).

This PR is to address the following issues:
https://bugzilla.redhat.com/show_bug.cgi?id=1131726
https://bugzilla.redhat.com/show_bug.cgi?id=1145776
https://bugzilla.redhat.com/show_bug.cgi?id=1145778
https://bugzilla.redhat.com/show_bug.cgi?id=1139433
https://bugzilla.redhat.com/show_bug.cgi?id=1131724
https://bugzilla.redhat.com/show_bug.cgi?id=1147669

As we're adding more and more purge settings, the first commit in the PR creates a new "Advanced Purge Settings" section (hidden by default) in the System Settings view in order to group them all.