Check integration of orbitals / electron / spin density

[ghutchis]

Some orbitals or electron density are diffuse and the standard padding isn't large enough.

• [ ] Allow the user to adjust the padding for cube / surface generation
• [ ] Check the integration of the orbital / density to see if it matches (e.g., 2 electrons for filled orbitals, etc.)

In some cases, the new distance cutoff check can help (e.g., the basis has very diffuse functions)