Dart interface is now able to write the surface pressure distribution.

Added vtk support in Dart api. Modified writing of boundary layer slices and introduced new argument of blast - writeSlices - which indicates vtk where to extract cps. The feature is not yet available for the boundary layer slices as this would require interpolation in the viscous solver.

dart module is added to the python path and can be imported when running test cases

Fixed API, dart interface and prevented segfault if the number of sections is not imposed correctly.

Contains 2D and 3D developements as well as the api.