Support conda-forge vtk binaries

[kwabenantim]

Description
The PyChaste conda package currently depends on a custom-built VTK because:

• PyChaste only supports VTK <= 7.x.x at the moment, but conda-forge binaries for VTK 7 are only available for Python2.
• The VTK binaries from conda-forge use TBB instead of MPI.

Switching to the conda-forge pre-built VTK binaries would simplify dependencies for the PyChaste conda package.

It would also allow the use of OSMesa based VTK builds available from conda-forge, which would help remove reliance on the Xvfb workaround for off-screen rendering in notebooks. From #8:

Moving to an osmesa-based vtk build would be a cleaner future solution ...

To Do

• Add PyChaste Support for VTK 8 #23
• Add PyChaste Support for VTK 9 #24
• Support VTK built with TBB
• Support VTK built with OSMesa