Add support for concentric filling

[arjanmels]

Added support for concentric filling: The vias will be aligned with the edges of the areas. There are option to entirely fill overlapping areas with vias, to only add an outer ring or to only add an outer ring to the outside (so not along holes).

In addition the delete vias function is implemented.

Full area fill ("Concentric"):

Along edges both outside and inside ("Outline"):

Along edge outside edge only ("Outline (No Holes)"):

And for reference the original modes:

Rectangular ("Rectangular"):

Random rectangular ("Rectangular", with random switch):

Star ("Star"):

Random star ("Star", with random switch):

[jsreynaud]

Thank you for your commits !