[glyphs2ufo] add --no-propagate-anchors CLI option

[anthrotype]

Fixes #906

Currently glyhps2ufo does the anchor propagation by default, unless the .glyphs file contains "Propagate Anchors" custom parameter set to false. There is a --propagate-anchors option but it doesn't do much since we do it even when the custom parameter is missing.

This PR adds the mutually exclusive --no-propagate-anchors which will disable this without having to modify the .glyphs file to add the custom parameter.

[anthrotype]

I also considered changing the default so that glyphs2ufo script does not do the anchor propagation unless requested (via either custom param explicitly set to true or via CLI option) but that would change the current behavior and might get unnoticed producing other issues down the road, so I simply added the negative option without changing the default behavior.

[schriftgestalt]

I remember some mention of a cli option to control if the ufo is intended to be used to build binary files or to work on the source (and potentially round trip back). That would make the "minimal" option obsolete, too.

That option would trigger a lot preprocessing, decomposing of anchors, corner components, built kern/mark features …

So by default when you run glyphs2ufo, it would keep the data as roundtripable as possible. And if you run fontmake -g …, it would always preprocessing everything.