Perpendicular flap with shell element

[Crazy-Rich-Meghan]

• Use shell mid-plane to represent elasticity
• Coupled with OpenFOAM via vertex-vertex communication method
• Use volume for visualization

[hverhelst]

There are quite some left-over sections commented out, and gsDebugVar calls left in the code. Would be nice to give it a small clean-up.
In addition, try to comment a bit more sections. Maybe we can accompany the file with a .dox file, so that it'll be documented immediately; this is a good practice anyay.
Lastly, it would be nice to have the update of the shell volume (inside the time-loop) as just a function call,i.e. constructShellVolume(mid_surface,thickness) (and maybe some direction to indicate which direction the thickness acts). Is this possible?