remove app_label for D1.7 // Introduce ContractInstance

ContractInstance model being an instantiation of the abstract Contract
which is displayed under Offer conditions in Economica.  Once the
Contract moves into Commitment flows, such as Order/Invoice
Payment/Fulfilment – then we need it to be instantiated with the
relevant Agents and put under Workflow or State Machine
this belongs in cars
Candidate settings for an REA ecosystem.

Define the root Agent model for the given economic system.  And the
Reporting Agent ID – which is where all reciprocity and exchange
dualities are in perspective.