Merge branch 'cleanup/3.7' into 'master'
[exercises] Updates/cleanup for 3.7
See merge request !143 (merged)
(cherry picked from commit b4c16461)
9ae93f05 [exercises] upgrade license 922b3dc7 [cleanup] Update exercise basic ede82630 [cleanup] Use constexpr in instead of enum 12856e89 [cleanup] Remove clutter 0da6c871 [cleanup] Fix spelling mistakes with codespell b162c1af [cleanup] Use more static constexpr int instead of enum 4ee41735 [cleanup] Remove ctime and dumux message 0a08f5e3 [cleanup] Use new solvers, no setPreviousSolution, initialize c2ad627a [cleanup] Replace enums with static constexpr 608e50a5 Update some code snippets in readme