Fold validator root(s) into state root (app hash) about celestia-core

[liamsi]

The decision was made to keep the validator hashes as they are in the header for now.

[musalbas]

For any modifications we need to make, I think it's best to do them in a way that is compatible with the philosophy of Tendermint, where the ABCI client is responsible for consensus and the ABCI server is responsible for the state machine.

[liamsi]

(1.) would mean following above mentioned philosophy more than the tendermint implementation itself. Probably the desired approach if it isn't difficult to do inside the SDK (need to check).

[liamsi]

The main work for this will happen in celestiaorg/cosmos-sdk#7 but let's keep this issue around as this means we also need to change the light client to understand the subtree of the state tree in the app that contains the validators.