Verify Header in Wasm light client

[ljoss17]

Closes: #216

Following #203 which added a SignedStarknetHeader, this PR adds a public key field to the client state and uses the public key to verifies the header and signature in the SignedStarknetHeader

[ljoss17]

For verify_membership_raw and verify_non_membership_raw,

ibc-starknet/light-client/ibc-client-starknet/src/client_state/common.rs

Lines 50 to 69 in 4c63248

	fn verify_membership_raw(
	&self,
	prefix: &CommitmentPrefix,
	proof: &CommitmentProofBytes,
	root: &CommitmentRoot,
	path: PathBytes,
	value: Vec<u8>,
	) -> Result<(), ClientError> {
	Ok(())
	}
	fn verify_non_membership_raw(
	&self,
	prefix: &CommitmentPrefix,
	proof: &CommitmentProofBytes,
	root: &CommitmentRoot,
	path: PathBytes,
	) -> Result<(), ClientError> {
	Ok(())
	}

, we don't have access to the Context, thus to the secp256k1_verify method. One solution would be to use the secp256k1 library but this causes the Wasm contract to be too big to upload on Osmosis