Change the way `alpha` is processed

[nwlandry]

As of right now, edge colors are not handled correctly in draw. If a user does

xgi.draw(H, edge_fc=(0, 0, 0, 0.2), alpha=0.4, edge_ec=(0, 0, 0, 1))

then alpha will override both values. The reason for this is that we are attempting to leverage the PatchCollection alpha keyword, which does not offer per-edge flexibility. I propose that we remove the alpha keyword, and have some logic in place for making the default alpha values of edge_fc and edge_ec be 0.4 and 1 respectively, but that individually specified alpha values will override these defaults.

I think that we can handle this by converting everything to a 4-tuple before passing it to PatchCollection and removing the alpha keyword.