ufoLib/Defcon/Fontforge based import to hava a way to set contour identifieres

xml pretty printing for *.plist and *.glif
prepared b for metapolator
add "b" to imported subset
move centerline-to[...].cps back to the cps root directory, use the version created by metapolator
upgrade fontforges ufo_v2 to ufo_v3

This uses roboFabs ufoLib and defcon from their ufo 3 branches, which
I had to change at some places. I will create pull requests.

Here are thr links to my forks:
https://github.com/graphicore/defcon/tree/ufo3
https://github.com/graphicore/robofab/tree/ufo3k
the new import ufo directories have different names to be ignored
new xml pretty printing
import "b"
define general rukes for the new 'MOM Outline' element
setup b