Address Dumux issue 648 in the course (separate properties header)

see dumux#648 (closed)

TODO:

• Separate the properties for the Basics exercise ( !90 (merged) ).
• Separate the properties for the main file exercise ( !91 (merged) ).
• Separate the properties for the runtime parameters exercise ( !92 (merged) ).
• Separate the properties for the grids exercise ( !94 (merged) ).
• Separate the properties for the properties exercise ( !95 (merged) ).
• Separate the properties for the fluid systems exercise ( !96 (merged) ).
• Separate the properties for the coupling free and porous medium flow exercise ( !97 (merged) ).
• Separate the properties for the discrete fracture modelling exercise ( !98 (merged) ).
• Separate the properties for the biomineralization exercise ( !93 (merged) ).