Small refactor of plotting

[jnsbck]

Fixes #465 and refactors some plotting functionality.
Changes:

• rm morph_plot_kwargs, rely on **kwargs instead.
• renamed kwarg "col" -> "color" for consistency with pyplot.
• Refactor Network.vis
• cleanup of code (use new View functionality) and removal of unnecessary kwargs
• rm _to_graph since it is obsolete now (replaced by scatter, which might be not as nice as the graph plotting, can be added back in though.). Since networkx is not used currently, this could also be removed as a dependency (until Add support for graph operations #355 makes it in at least)
• disentangle moving and visualizing of cells, by adding arrange_in_layers. I think this is more clear and seperates out the additional kwargs of vis.

To get the same as net.vis(layers=[3,3]) one now has to do.

net.arrange_in_layers([3,3])
net.vis()

This now also works for both detail="full" and detail="point" and even for dims=[0,1,2] (not that this would be necessary). In general network.vis should feel more similar to cell.vis.

[jnsbck]

I think we can ignore regression tests not passing. they will get an update see #540, which should make it less annoying to get them to pass.

[michaeldeistler]

Thanks for this, all looks good!

[jnsbck]

fyi @kyralianaka in case you are using this.