Validate genesis blocks on network change

[tuliomir]

After #660, all registered tokens and registered nano contracts are cleared from the app when the network is changed.

However, the change may be happening for nodes within the same network, like changing the fullnode from node1.mainnet to node2.mainnet, which shouldn't trigger a registered token cleanup. This is an edge case of the issue raised by #385

To implement this, we could read the hashes of the genesis block obtained from the fullnode status request and compare to the previous network. If both are the same, we can assume the network hasn't changed and the registrated data cleanup should not occur.