refactor and add named statements / pods / origins

[gubsheep]

• the Optionals in statements can now be arrays
• Entry is now a convenience struct that holds a key and value, but is never actually used in PODs - PODs just have statements
• there is now just a single POD class that is not generic over anything
• POD has a PODPayload and a PODProof. the PODPayload is always a collection of Statements. the PODProof is an algebraic type that is either a SchnorrProof or an OracleProof
• origins and statements now have string names, in addition to numerical IDs. in operations they can now be referenced by names and not just by IDs; in fact, numerical IDs should never be touched by anyone using the lib. numerical IDs are automatically generated from names by sorting origins / statements lexicographically by names, and remappings take this into account.
• renamed “GOD” to “Oracle”
• some refactoring done to make certain things clearer - we now have GPGInput, OperationType, and OperationCommand
• implemented the Contains operation and RenameContainer operation
• added good boy POD test that fully implements the example written out in https://hackmd.io/@gubsheep/BJPsRyFTR