App: Interpolation between geometries

[danielhollas]

Create a simple app that takes two geometries of the same molecule as an input, and produces interpolated geometries in between.

Options for interpolation:

• Linear in XYZ (optional, only to see how bad it is)
• Linear Interpolation in Internal Coordinates (LIIC) - this is what people are now using. Use openbabel?
• Geodesic interpolation, implemented in https://github.com/virtualzx-nad/
  geodesic-interpolate

Other inputs:

• nsample: Number of interpolated geometries

In the future, provide Energy scan on top of the interpolated coordinates as the next step.

[danielhollas]

We will have to modify the first StructureSelectionStep to handle two Structure Managers at once, for the initial and final geometry.

https://github.com/ispg-group/aiidalab-ispg/blob/main/aiidalab_ispg/app/qeapp/structures.py