* Rename AggregateCommands to IssuanceCommands
* Reorder comparisons to be consistent
* Rename verifyDefaultCommand to verifySetLifecycleCommand
* Rename currency to issued/product
* Add note about needing to rethink timestamping
* Rename issuer to obligor, and owner to beneficiary
* Move lifecycle inversion code into SetLifecycle command
* Correct comments regarding cash states
* Rework description of contractHash parameter
* Fixes 'netting equal balances due between parties', and add further netting tests
* Separate calculations involving issued products and the underlying product
* Use signed transactions in obligation tests
* Add verification tests for changing lifecycle
Add a new Obligation contract, modelling an obligation to send an amount
of something (currently limited to cash) by some future point. Obligation
contracts introduce the concept of one contract being aware of other
contracts, and common interfaces for state objects so other contracts can
interpret them meaningfully.
