Updated the policy part of the language. Very early support for policies
and rules
Cleaned up request language and code generator.

Still doesn't behave properly when a type of attribute (subject, 
action, resource or env.) is empty
Updated attributes declaration and use in requests.

Now, attributes must declare whether they are subject, action, request 
or environment attributes, and requests must use the right kind of
attributes.
Updated ecore & gencore models