meshdata.py and an example use it

Some change in meshdata.py
- Add cone and arrow mesh primitive
- add () in line 401 because it's a function
- modifie meshdata.vertices becaus they are a conflict with vertex_normal and face_normal call

Add an example to manipulate the mesh primitive 
- I have a problem with the primitive_mesh_viewer.Canvas.setData because this function doesn't change the camera view. Look in the code and help me please ...
I am still trying to wrap my head around why this is necessary. If we already have `vertices_indexed_by_faces`, why is it useful to have an array of faces indexed to that? This would just be `np.arange(Nf*3).reshape(Nf, 3)`?