[test][tracer] restructure and improve tracer conservation test

Outsource properties to a separate header. Move function to check
conservation from problem to main. Improve variable names. Switch
to one space dimension, adapt simulation time interval. Throw an
exception if tracer is not conserved.
5 jobs for !2767 with fix/tracer-conservation
latest detached
Status Name Job ID Coverage
manual full-dune-2.7-clang
manual full-dune-2.7-gcc
manual full-dune-master-gcc
manual minimal-dune-2.7-gcc
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