early global reservation lookup for classes

The idea is to introduce a new global boolean parameter (*) which:

• makes global reservations to be search as soon as possible
• add reserved classes to the query
• perform classification
• check the drop class (if the query is in the class drop it)
• use classes as guards for subnets and pools

This implements with other goodies the drop using reservations (more convenient in some cases than long classification expressions) asked by some customers.

This change should address #1973 (closed), #1543 (closed).