Merge branch 'feature/materialsystem' into 'master'

[materialsystem] add Bea's material system slides

See merge request !47

slides/README.md

@@ -6,3 +6,4 @@ Click on the links to download the slides
 * [Slides on the problem file](./dumux-course-problem.pdf)
 * [Slides on runtime parameters and grids](./dumux-course-runtimeparams-grids.pdf)
 * [Slides on properties](./dumux-course-properties.pdf)
+* [Slides on the material system](./dumux-course-materialsystem.pdf)