Improve templates and cleanup

[andrewwinters5000]

• Run the spring smoother after reflection across a symmetric boundary Smooth symmetric mesh #155
• Allow to reflect across multiple lines, e.g., a vertical line and then a horizontal line to take the mesh of a quarter of a domain and create the entire domain mesh.
• Mesh cleanup to fix corner template, e.g., after a symmetric mesh generation. Came up in the design of the nozzle tutorial during TRUDI in Cologne. A figure with an example of such a cleanup region is given below.