implement ignore_layers, force_macsuck, force_arpnip config settings (#1002)

* implementation of ignore_layers, force_macsuck, force_arpnip and macwalk

* use new WalkJobs view to get devices needing macsuck

* also new query for discoverall, arpwalk, nbtwalk

* faux record has a last_defer stamp so we can see when the backend started

* fix typo

lib/App/Netdisco/Worker/Plugin/Arpnip/Nodes.pm

@@ -65,7 +65,6 @@ register_worker({ phase => 'store' }, sub {
     $device->ip, $v6;
 
   $device->update({last_arpnip => \$now});
-  $device->update({layers => \[q{overlay(layers placing '1' from 6 for 1)}]});
 
   my $status = $job->best_status;
   return Status->$status("Ended arpnip for $device");