OpenSCAD Module: bugfixes and improvements

if more than 14 digits are given don round in general,
but test for <eps only.
refine before extrusion
support polyhedron faces which replaces polyhedron faces
importCSG round rotations
don't call Draft.makecircle and makeprism as they trigger a recompute
use group placholder for objects with no children
move removesubtree to OpenSCADUtils
add resize and offset keywords
add OpenSCAD_ExplodeGroup command
add OpenSCAD_IncreaseToleranceFeature
change refine shape logo