ENH: added bin/tools/ change-sitedir.sh, change-userdir.sh

- can be useful with compiling additional OpenFOAM programs
  that use FOAM_USER_APPBIN, FOAM_USER_LIBBIN for their build,
  to avoid conflicts with the normal user bin/lib files.

- or to force relocation of FOAM_SITE_APPBIN, FOAM_SITE_LIBBIN
  during packaging of OpenFOAM