Merge branch 'fix/problem-slides' into 'master'

[slides][problem] Make setup image accessible in slides.

See merge request !245

slides/problem.md

@@ -6,7 +6,7 @@ title: DuMu^x^ applications
 
 ## Simulation goal
 
-<img style="float: right;" src="../exercises/extradoc/exercise1_setup.png">
+<img style="float: right;" src="img/exercise1_setup.png">
 
 ## Gas injection / immiscible two phase flow