Fix python wheels

[lnotspotl]

This PR fixes wheels wheels downloaded from the Python Package Index (not installed from source using pip install -e .)

Without these changes, importing unitree_sdk2py leads to errors as b2, a package imported in the global __init__.py, is in reality not a python package, its __init__.py is missing and thus b2 is not installed.

Finally, pygame is added as a dependency as it is use in utils/joystick.py

[jaeykimusa]

Yes, this solves the issue. @xiaoliangstd