feat(order_utils.py): sign_hash() (#1254)

Also moved is_valid_signature() into main package module, for
simplicity.

Also consolidated a handul of in-line pylint disable directives into the
.pylintrc config file.

python-packages/order_utils/test/test_signature_utils.py

@@ -3,7 +3,7 @@
 import pytest
 from web3 import Web3
 
-from zero_ex.order_utils.signature_utils import is_valid_signature
+from zero_ex.order_utils import is_valid_signature
 
 
 def test_is_valid_signature__provider_wrong_type():