SessionDB is an interface that gives helper methods for how privacy
mapping should be done. A mock for SessionDB is added to save on some
code repetition, the privacy flags functionality is used in a later
test.
This commit adds a new Action type to the firewalldb package along with
Serialization and Deserialization methods for it. It also adds
ListAction and ListSessionAction methods to the DB which can be used to
paginate through the actions. Various interfaces are also added that
will be used by `rules` to access certain RuleActions.