pyvista/pyvista: Bug Fixes and General Cleanup

This release is primarily full of bug fixes and general cleanup around the filters and plotting methods. Bug Fixes Fix points ordering issue with gridded datasets Fix issues with overlapping colorers (see #319) Fix rare bug when scalars are the wrong size Handle panel runtime errors on import (see #322) Fix smooth_shading issue for non-PolyData datasets Fix subplot indexing issues (see #346) Changes Memory footprint is improved (see #338) panel notebook rendering is now off by default New downloadable examples! Filters were overhauled into their own module and generalized across datasets (see #323) Improved control over axes widgets (see #334 and #342) Improvements to add_mesh and add_volume docstrings Deprecate BasePlotter.plot (see #341) Enable use of poly lines with PolyData (see #344) Add more lighting controls (see #343