Fraud Proof generation and partial verification using IAVL store

[Manav-Aggarwal]

Cover Fraud Proof Generation and the first two levels of verification.

Possibly consolidate code across PRs from celestiaorg#245 while replacing the usage of the SMT store with the IAVL store.

The third level of verification needs the functionality to set up a BaseApp from a Fraud Proof. This requires the ability to create IAVL Deep Subtree. We can add placeholders for these IAVL Deep Subtrees which can be added once rollkit/iavl#1 is wrapped up.