Cleaning up old FSI code and standardizing algorithm

[eyoung55]

The current FSI implementation will:

• Not move the nodes of the structural mesh
• Use an undeformed copy of the fluid mesh as an intermediate step to: (1) match nodes between the undeformed structure and the undeformed fluid (initialized to match, and never changes) and then (2) match nodes between the undeformed fluid and the deformed fluid (same DoF numbering since they are identical copies of the mesh, where the deformed copy has its node positions modified over time)
• Project stresses calculated on the deformed fluid into the reference frame of the undeformed mesh (e.g., a stress normal to the surface of the deformed panel needs to be rotated such that it is still normal in the reference configuration)

[arswalid]

to be tested:

• pytests
• FSI flag