[Geometry] Move all geometry headers to their own folder

dumux/CMakeLists.txt

dumux/geometry/CMakeLists.txt

dumux/geometry/boundingboxtree.hh

dumux/geometry/diameter.hh

dumux/geometry/distance.hh

dumux/geometry/geometricentityset.hh

dumux/geometry/geometryintersection.hh

dumux/geometry/grahamconvexhull.hh

dumux/geometry/intersectingentities.hh

dumux/geometry/intersectionentityset.hh

dumux/geometry/intersectspointgeometry.hh

dumux/geometry/intersectspointsimplex.hh

dumux/geometry/makegeometry.hh

dumux/geometry/normal.hh

dumux/geometry/refinementquadraturerule.hh

dumux/geometry/triangulation.hh