added Find*/Get* cmake modules

@ Find*: uses the environment variables to find and build the vienna libraries
@ Get*: uses CMake's externalproject_add-git option to automatically download and compilie the ViennaLibraries
  -> only the git download is implemented right now, still need to set the includes/library paths
added ViennaFVM cmake find/get modules + fixed include paths of cmake modules

nin2d example compiles (though simulator is still empty)
working on viennamini::material_library

dummy ready, already imports files according to their fileending
automatically via viennamaterials.
nin2d example builds and links iwth the new cmake build system