Subnet and Boot config addon

The goal of this project is to allow the specification of an attribute
for the nodes representing subnets (subnet = school or lab). 
This attribute will be used to detect the computer location on the autocreate.php script.

To install : 
- Copy autocreate.php.subnet to .../mille-configurator/Terminal/autocreate.php
- Copy SubnetNodeFinder.php to .../mille-configurator/Admin/util
- Execute mxt_attr_DB_Mille.sql on the mille database


mille_attr_DB_Mille.sql add these attributes :

NODE_SUBNET : Specify the associated subnet of a node.
PXECONFIG : Boot configuration used by pxeconfig.
