Add dependency file for Binder to use, including optional dependencies

[hakonanes]

We should add a file for Binder to use when setting up the environment, like is done in orix: https://github.com/pyxem/orix/blob/develop/environment.yml.

[hakonanes]

I think we have to take the approach of https://github.com/pyvista/pyvista-examples to enable PyVista on Binder, because I keep getting an erorr message stating that libGL1.so isn't available (cannot import vtk nor pyvista).