devcg: move behavior and exceptions into its own structure

This patch is in preparation for the next one that will allow saving locally
set rules.

Signed-off-by: Aristeu Rozanski <aris@ruivo.org>
devcg: make dev_exception_ functions to use lists

In preparation for having active and locally set list of rules.

Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>
devcg: save locally saved settings

Whenever writing rules in the current directory, save these rules so it
can be used whenever parent's rules change. This patch prepares for
revalidating the local rules based on parent's current state, which is
not only needed to retain whenever possible the local settings but to
allow moving the group to another part of the tree.

Signed-off-by: Aristeu Rozanski <arozansk@redhat.com>