ODRL as nodes on a graph #129

This is an example of common policy use cases, where the ancestor contains some common rules that the descendants use, supporting better lifecycle management for the creator.

To showcase how "everything is a graph", in this example:

• Rules, constraints, refinements, assets, etc. exist independently from policies
• Permission1 and Permission2 are equivalent (the outcome of the refinement applied by P2 is the same as the set in P1)
• The refinement for Permission2 and Prohibition1 is also the same node
• One rule of class Duty can be the duty/remedy/consequence for multiple rules in multiple policies

(note: for simplicity of the graph, actions are not shown, but permission1 and permission2 have the same action(s) to be equivalent, assignees are all the same)