Add reader for Circle CVI workspaces

[p-j-smith]

Changes made:

• Added a reader for Circle CVI workspace file
• Creates a pyvista.PolyData mesh from the contours defined in the workspace file along with associated dicom files
• Added an example of how to use the reader
• Optionally returns a pandas DataFrame containing metadata about the dicoms used in constructing the mesh
• Creates either the epi or endo surface mesh, or both