Folder names in freeflow

the NavierStokes, NavierStokesNC, NavierStokesNI models are defined in the folder staggered, staggerednc, staggeredni which doesn't seem appropriate. In fact the physical models/TypeTags shouldn't know anything about the discretization. So the folder names "navierstokes", "navierstokesnc", "nonisothermal" seem more appropriate.