Add function to set equilibrium states

[Jarvellis Rogers]

Add a function to FFEA that allows users to give FFEA a topology file and set that as the equilibrium state for an FFEA system, and then use this to allow users to interact with the system during simulation.

For example, a user could set an equilibrium state for a protein and then apply a push force to see how that would affect it.

Additionally if FFEA simulations could run in virtual reality, this function would allow for users to have more direct interactions with simulations.

This proposal was suggested in the evaluation report for FFEA 2.7.2.