feat(order_utils.py): ERC20 asset data encoding and decoding

In addition to the ERC20 codec, also:

Stopped ignoring type errors on 3rd party imports, by including
interface stubs for them;
Removed the unimplemented signature-utils module, which was just a
stand-in when the python project support was first put in place.

https://github.com/0xProject/0x-monorepo/pull/1144

python-packages/order_utils/stubs/distutils/command/clean.pyi

@@ -0,0 +1,7 @@
+from distutils.core import Command
+
+class clean(Command):
+    def initialize_options(self: clean) -> None: ...
+    def finalize_options(self: clean) -> None: ...
+    def run(self: clean) -> None: ...
+    ...