reimplementation of draw_voroinoi

[quaquel]

This reimplements draw_voroinoi and makes it behave identically to draw_hexgrids. This, therefore, removes cell_coloring_property from the Voronoi grid. It also adds the draw_grid boolean to draw_voroinoi which is also available for all other discrete spaces.

Any future work on further developing the API for controlling how to draw a space itself such as #2438 and #2557, now at least can start from an underlying consistent code base.

Before

After

Closes #2437 and #2549