Add IBC Contract

[arhag]

This is the IBC contract that supports IBC with the new Savanna consensus. It should still be able to do action proofs for blocks prior to the Savanna transition. But it does not need to support finality proofs for the legacy consensus algorithm.

Create the structure of this initial repo to support building other contracts in addition to the IBC contract. For now the IBC contract is only needed in this repo. But in the future other reference contracts related to Savanna consensus may be added such as a finality violation verification contract.