Feature: Lights and Shadows Merge

[rinftech-github]

Squashed and merged with master. Should replace https://github.com/maartenbreddels/ipyvolume/pull/308

Added lighting and shadowmap support for plot_mesh, plot_trisurf, plot_surface. Scatter supports lighting but does not support shadowmapping because of an existing Three.JS issue: https://github.com/maartenbreddels/ipyvolume/issues/276

I encountered scaling issues with mesh and scatter plots caused most likely by previous pull request changes.