[material]

- added doxygen comments and cleanup of defaultcomponents.hh
- improved documentation of constant.hh

[test]
- added units in test_navierstokes.input

reviewed by natalies



git-svn-id: svn://svn.iws.uni-stuttgart.de/DUMUX/dumux/trunk@15420 2fb0f335-1f38-0410-981e-8018bf24f1b0