attempt to refactor the entire color system to simplify & centralize
fix build i just broke
add test3dexport tests and colorscheme tests
Merge branch 'test3dexport' of github.com:openscad/openscad into test3dexport

Conflicts:
	tests/regression/export3d_off_test/example001-expected.png
	tests/regression/export3d_off_test/example002-expected.png
	tests/regression/export3d_off_test/example003-expected.png
	tests/regression/export3d_off_test/example004-expected.png
	tests/regression/export3d_off_test/example005-expected.png
	tests/regression/export3d_off_test/example009-expected.png
	tests/regression/export3d_off_test/example010-expected.png
	tests/regression/export3d_off_test/example011-expected.png
	tests/regression/export3d_off_test/example014-expected.png
	tests/regression/export3d_off_test/example016-expected.png
	tests/regression/export3d_off_test/example019-expected.png
	tests/regression/export3d_off_test/example020-expected.png
	tests/regression/export3d_off_test/example023-expected.png
	tests/regression/export3d_off_test/polyhedron-nonplanar-tests-expected.png
	tests/regression/export3d_stl_test/example001-expected.png
	tests/regression/export3d_stl_test/example002-expected.png
	tests/regression/export3d_stl_test/example003-expected.png
	tests/regression/export3d_stl_test/example004-expected.png
	tests/regression/export3d_stl_test/example005-expected.png
	tests/regression/export3d_stl_test/example009-expected.png
	tests/regression/export3d_stl_test/example010-expected.png
	tests/regression/export3d_stl_test/example011-expected.png
	tests/regression/export3d_stl_test/example014-expected.png
	tests/regression/export3d_stl_test/example016-expected.png
	tests/regression/export3d_stl_test/example019-expected.png
	tests/regression/export3d_stl_test/example020-expected.png
	tests/regression/export3d_stl_test/example023-expected.png
	tests/regression/export3d_stl_test/polyhedron-nonplanar-tests-expected.png