Dash-vtk

Changed
* [Demos](https://github.com/plotly/dash-vtk/pull/16): removed headers, updated layout sizes, remove unused files
* `demos/usage-vtk-cfd`: update viz on drag
* `demos/pyvista-point-cloud`: faster loading by lowering sampling
* `demos/slice-rendering`: faster loading by removing volume rendering
* `README.md`: Change relative links to URLs
* `docs/CONTRIBUTING.md` ([commit](https://github.com/plotly/dash-vtk/pull/15/commits/0ec656e20b7e34e77bab7c573748e2842eba0d5f)): Various clarification and improvements

Fixed
* Simplified imports in `dash_vtk.utils.vtk` to only load necessary modules from `vtk`. This avoids `libGL.so.1` since server side rendering is not needed.

Added

* PyPi description auto-generated from `README.md`

Changed
* Use `package.json`'s files instead of `npmignore`
* Change order of instructions in `docs/CONTRIBUTING.md`

Fixed
* Update `setup.py` to include `utils` directory when upload to PyPi.

This is the initial release.