Widgets, Point Picking, and Tables

New Features

• Add full support for widgets in the rendering scene! (See #360)
  • Box widget - Create a box in 3D space. Includes a convenience method for clipping meshes
  • Plane widget - Create an implicit plane in 3D space. Includes a convenience method for clipping and slicing meshes
  • Slider widget - Add a slider bar to the render window. Includes a convenience method for thresholding meshes
  • Line widget - Create and orient a line in 3D space.
• Point picking (see #362)
  • Single point picking on meshes and in 3D space
  • Trace lines across meshes using a geodesic path
  • Trace lines through a scene by picking points on meshes or in 3D space
  • Trace out horizon surfaces
• Wrap the vtkTable class (see #274 and the new pyvista.Table class)
• Add a structured grid cylinder helper method (see pyvista.CylinderStructured) which works creates a pyvista.StructuredGrid mesh in the shape of a cylinder.
• New .ribbon() filter for PolyData objects - create surfaces (“ribbons”) from lines
• interpolate_befor_map is now set too True as default (see #363 and this example for details)

Bug Fixes

• Resolve issues with the lines_from_points helper methods (see #357)
• Fix an issue when fetching null points on datasets