Install headers in same folder structure, not ug/

CMakeLists.txt

dune/uggrid/CMakeLists.txt

dune/uggrid/domain/CMakeLists.txt

dune/uggrid/gm/CMakeLists.txt

dune/uggrid/low/CMakeLists.txt

dune/uggrid/numerics/CMakeLists.txt

dune/uggrid/parallel/ddd/CMakeLists.txt

dune/uggrid/parallel/ddd/basic/CMakeLists.txt

dune/uggrid/parallel/ddd/ctrl/CMakeLists.txt

dune/uggrid/parallel/ddd/if/CMakeLists.txt

dune/uggrid/parallel/ddd/join/CMakeLists.txt

dune/uggrid/parallel/ddd/xfer/CMakeLists.txt

dune/uggrid/parallel/dddif/CMakeLists.txt

dune/uggrid/parallel/ppif/CMakeLists.txt