Separate inner and outer boundaries

In the current version inner and outer boundaries are set in a unique routine: for example open boundaries means inner and outer open etc ..

However, for some uses it is interesting to choose inner open and outer evanescent for example, as in issue 634

In order to avoid to have a new boundary condition just to mix inner and outer boundaries, we separare them in this branch.

The aim is also to have the same boundaries for 2D and 3D simulations (it makes it simple for the user to choose the boundary conditions)