Add Font Awesome through Python package

[gyli]

Font Awesome v6 now provides Python package on Pypi https://pypi.org/project/fontawesomefree/#description

Add Font Awesome through Python package, so no need to add a copy of otf files in PyWaffle.

This solution might not reduce the content that need to be downloaded when installing, and is not able to use system's font first (#25), while it does avoid some unnecessary downloads when there are other Python packages also using Font Awesome.