Update support wheel with universal flag

In the `IOTile` object there is a support wheel member that is used to know if a component has python packages and what the wheel that is generated should be called. Currently this assumes it will be a python 2 wheel which ends in .`py2`. When `ioitile-build` is run on python 3 it generates a `.py3` wheel. This means running `iotile-build` on a mix of python 2 and python 3 will not work unless the wheels are marked as universal.

So:

- [ ] Add a `python_universal` boolean to module_settings.json to trigger building universal wheels
- [ ] Check for that boolean in `pythondist.py` in `iotile-build` and enable universal wheel building
- [ ] Check for a mix of python 2 and python 3 wheels in `iotile build` and fail the build since they are incompatible