Bug 23681: (QA follow-up) Proper handling of default option

Bug 23681: (QA follow-up) Proper handling of default option

This patch removes the 'can_be_added_manually' flag. Only non-system
restriction types can be added manually, so we exclude is_system instead
of having two flags. (And we set the 'Manual' that's added at install
time to default but not system).

We then add proper handling for setting the default manual restriction
type in the management page and set the dropdown list to use that value
by default.

Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>