Base class for the server implementation of the service Firewall.
Firewall resources are used to define a collection of access control rules
for an Application. Each rule is defined with a position which specifies
the rule's order in the sequence of rules, an IP range to be matched against
requests, and an action to take upon matching requests.
Every request is evaluated against the Firewall rules in priority order.
Processesing stops at the first rule which matches the request's IP address.
A final rule always specifies an action that applies to all remaining
IP addresses. The default final rule for a newly-created application will be
set to "allow" if not otherwise specified by the user.