Put property definitions in tests (examples/applications) in separate header

To make another step away from the problem-does-everything-mentality that was common (and a necessary evil) in dumux 2, I suggest to put the property definitions into a separate header. There are not connected in any way to the Problem class, so IMO they shouldn't be defined in the problem header. For the purpose of re-usability they also shouldn't be directly coded in the main file.

Edit: Result from the vote: We want to advertise putting properties in a separate header.

• Separate properties into properties.hh for the examples (milestone 3.2) !1933 (merged)
• Separate properties into properties.hh for the dumux-course (milestone 3.2) course#24
• Separate properties into properties.hh for the dumux-lecture (milestone 3.3) lecture#15
• Separate properties into properties.hh for the tests (milestone 3.3)

This doesn't have to be in one go. If someone edits a test anyway feel free to do this change as well.