automatic dhcp_scope detection

Every network now can loosely have a 'dhcp_scope' value associated with
it. This is occomplished via first looking in the network's keyvalue
store for a 'dhcp_scope' key and if that doesn't a possible scope value
is calulated by looking at the network's site/vlan.

During SREG creation the 'dhcp_scope' key will be set on any new
HWAdapters. The value will be set to the dhcp_scope value of the network
of the range that is selected from the ip-chooser widget.

DHCP scope key mismatches are highlighted in red.