application of known displacements to nodes

**Is your feature request related to a problem? Please describe.**
In addition to nodal and member loading I'd like to be able to apply a known nodal displacement to a structure, to examine the internal loading that arises from foundation settlement for example.

**Describe the solution you'd like**
At the moment I don't believe there's a way to do this - no purposely written sub/function that I've seen anyways. Is that correct? If so it's something I will work towards including, although I have a feeling it'll require much more familiarity with the existing code than I currently have, not to mention a better grasp of OOP.

Start by reviewing the existing nodal and member loading functionality in the VBA library to understand how loads enter the structural analysis. Done should allow a known nodal displacement to be applied and expose the resulting internal loading for cases such as foundation settlement.

Written by the indexing model from the issue text.