[tutorial] implement first draft of exercise 3

tutorial/ex3/CMakeLists.txt

...rial/ex3/binarycoefficients/h2omycompressiblecomponent.hh

tutorial/ex3/components/mycompressiblecomponent.hh

tutorial/ex3/components/myincompressiblecomponent.hh

tutorial/ex3/components/plotdensityfunction.py

tutorial/ex3/ex3_a.cc

tutorial/ex3/ex3_a.input

tutorial/ex3/ex3_a_problem.hh

tutorial/ex3/ex3_b.cc

tutorial/ex3/ex3_b.input

tutorial/ex3/ex3_b_problem.hh

tutorial/ex3/fluidsystems/h2omycompressiblecomponent.hh

tutorial/ex3/spatialparams.hh