Consider converting from bower to yarn

[cosmicdreams]

The Bower folks keep telling us, "Don't use this". Someday we'll have to listen to them.

Many who use bower have already moved to yarn. We should consider doing the same.

[mlsamuelson]

@btopro Do you have any opinions here?

[mlsamuelson]

This pushes into territory outside of the scope of the D8 HAX integration, but I've shared the concern with @btopro. His response is essentially that all of the HAX world needs to make the jump in unison, and that the concern is on radar: https://twitter.com/btopro/status/997160042213335040