Merge branch 'feature/tutorial04-fixes' into 'master'

Fixes for tutorial 4

See merge request !59 (merged)

(cherry picked from commit 8f887972)

000899bc Merge branch 'bugfix/cleanup-exercises' into 'master' cf4fbe53 Merge branch 'cherry-pick-3cacd503' into 'releases/2.6' 7ed8fc9a Merge branch 'bugfix/second-cleanup-for-dune-course-2018' into 'master' f9b181a8 Merge branch 'cherry-pick-7849cc03' into 'releases/2.6' c2b380b0 Merge branch 'feature/doc-for-tutorial07' into 'master' 5e6a784a Merge branch 'cherry-pick-54cc60e8' into 'releases/2.6' dbe80ef9 Merge branch 'feature/more-fixes' into 'master' 4c42846e Merge branch 'cherry-pick-fbd00b9b' into 'releases/2.6' 02981650 Merge branch 'tutorial06_2018' into 'master' e647db4f Merge branch 'cherry-pick-5e54cfd9' into 'releases/2.6' 8b124350 Merge branch 'tutorial00_2018' into 'master' eb08bb2f Merge branch 'cherry-pick-3b9bbb50' into 'releases/2.6' 01a4f026 Merge branch 'feature/doc-for-tutorial07' into 'master' 2b5fc105 Merge branch 'cherry-pick-bce416a0' into 'releases/2.6' 2285d601 Some small fixes for wavefem.hh