Aerodynamic forces correction enhancements

[ngoiz]

This PR tranfsorms the aerodynamic forces correction functions to generators to be used in the coupled solvers. This is for cases where airfoil polars are defined (see updated Case Files documentation).

In this PR we include:

• Correct forces: transform functions to generators
• Bug fixes in polar corrections and full documentation
• Update to the aeroforcescalculator post-processor to output corrected forces and to output aerodynamic forces and moments. The latter are now written on a separate file moments_
• Changes to the aero data structure such that the aero forces expressed in the beam degrees of freedom are included in the aero time step

[ngoiz]

Thanks both for your comments. I think I have addressed all your points:

• Horrible aerotstep.aero_forces_beam_dof is gone and instead it goes into structtstep.postproc_nodes['aero_steady_forces] (or unsteady) which is then plotted in Paraview
• Opted to retain aero_tstep.body_steady_forces since those are a 6x vector and for each surface, which is useful in some cases and it doesn't go in nicely onto the postproc_node strategy as above. These are defined in the AeroTimestepInfo class.
• Adapted the AeroForcesCalculator postproc to run online and offline
• Moved the test to the polars tests /tests/uvlm/static/polars

I think this covers my changes. @ArturoMS13 once you are happy with the stability axes and your twisting wings I think this should be then good to go

[ArturoMS13]

Thank you for the contribution
I have double checked this implementation for wind turbines and it works except from the root regions. I will fix the root soon, but it is not a big deal so this PR can be merged.

[ArturoMS13]

Just some extra minor changes. Thank you for the contribution