cli should throw error if --chain-id not provided

[ebuchman]

Txs require --chain-id to be provided so it can be signed.

Note the chainid is not included in the tx itself, but it is part of the bytes that get signed to prevent cross-chain replay attacks.

Unfortunately, it means the error message just comes up as "signature verification failed" and we can't really detect why.

Thus, if the --chain-id is not provided, we should throw an error and tell the user it must be provided.

[cwgoes]

Can we load the chain ID automatically from the genesis file, if present?

[cwgoes]

Will the light client keep a genesis file with chain ID? democli init isn't implemented, not sure if that's intended to write genesis information or not.

[ebuchman]

Note we have to implement the basecli init functionality, which should set a chain id and other stuff like the node id and the initial validator set (to be socially authenticated).

See #822

[Onefox]

This problem is there again with gaiacli tx sign. No error is giving and a signature is produces that can not be broadcasted.