LedgerDSL(interpreter: L, notary: Party)
This is the class that defines the syntactic sugar of the ledger Test DSL and delegates to the contained interpreter,
and what is actually used in ledger { (...) }. Add convenience functions here, or if you want to extend the DSL
functionality then first add your primitive to LedgerDSLInterpreter and then add the convenience defaults/extension
methods here.