Visualize.glut_init: use glutPostRedisplay
Scene: separated from Visualize
Surface: show the right scene
Scene.string_of_vector: added
Scene: added map and fold functions for scene/face/vertices. Implemented center_scene with those.
Surface: center the scene prior to rendering it; don't use 'size'
Visualize.display_mesh: eliminated 'size' translation support
Surface: Altered perspective a bit (less of an effect)
RecVec, Scene: moved code from Surface
Surface: removed commented code
Scene: Vertices are now in a list, not in array

This is building way to a functionally updated scene
Scene.face.id added

This is to allow referring to a face by its id. mk_face_id creates such
ids.
Scene: face is no longer parametrizable for normal and color
Scene.face.face_id: renamed from id
Scene is now stored inside a map
Scene.face.face_id: removed. The face_id in FaceMap suffices. Maybe.
Scene.scene_of_function: renamed make_grid'
Scene: added an interface
Surface: eliminated unused value
Scene.face0: removed