Improve geometry and mesh for RANS computations

[acrovato]

In order to create a valid mesh for RANS computations, the surface mesh must be extruded to create a prismatic boundary layer. The geometry and the surface mesh must as smooth as possible. Some improvements could be made...
For the geometry:

• use a spline at the leading edge of the wingtip, and enforce that it is tangent to the leading edge
• use splines at the trailing edge to make it less rounded
  For the surface mesh:
• use a transfinite surface mesh
• use a Field attractor to refine the trailing edge locally

[acrovato]

Transfinite meshes are supported since v1.0.0 (ref. 08099d8)