Add traffic-control long-tail: mangle/accounting/tc_*

Storage + CRUD (migration 0008, model, id-keyed store, REST handlers) + compiler
rendering for mangle, accounting, and tc_devices/tc_classes/tc_filters/
tc_interfaces/tc_priorities, each owned by a device. (Nested tc option structs
deferred.)

internal/server/resources.go

@@ -63,6 +63,7 @@ func (s *Server) mountResources(r chi.Router) {
 	s.mountLongtail(r)
 	s.mountPerDevice(r)
 	s.mountPerDeviceL2(r)
+	s.mountTraffic(r)
 }
 
 // respondOne writes a single resource, mapping ErrNotFound to 404.