Added a plotting utility for aeroelastic modes

[ben-l-p]

This includes a new AeroelasticModal post processor which plots the aeroelastic modes, found from the linearised aeroelastic system. Whilst looking at the aeroelastic eigenvalues is useful for determining stability, this post processor is useful for investigating what the modes look like, which can be hard to interpret from a vector of complex numbers!

The output is similar to the Modal solver which plots the natural modes of the structure projected onto the aerodynamic grid as VTK files, however this here also includes the aerodynamic gamma terms for both the bound wing panels and the wake. As there is a phase component in the aeroelastic eigenvectors, I have included the ability to plot at evenly spaced points, which gives an animation of what the mode looks like. Please enjoy an example gif of the output below for the Pazy wing, however I have also validated it for the FLEXOP with more aerodynamic surfaces.

To keep it compatible with the Krylov reduction (allowing for much faster analysis) I was required to make small changes to the linear system source code, only so that gain matrices are propagated to the post processor as well as information about the original linear system states. It can be very interesting to see what aerodynamic features the Krylov likes to keep, and what it discards. I increased the default Krylov order from 1 to 4, because 1 usually gives very poor results.

I also removed some unused code here - the functionality of this solver should however be as before.