Improve compilation script for cases with DuMux

[Fujikawas]

With current compile-dumux-cases script, it can't compile when the case folders are newly cloned and contains no build-cmake folder. In the new ones, two options are offered: compile from zero or only recompile.

Checklist:

• I added a summary of any user-facing changes (compared to the last release) in the changelog-entries/<PRnumber>.md.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[IshaanDesai]

Looks good, I did not test it though, as I assume that is done. Just a small word change suggestion from my side. Please don't forget to add a changelog entry as this is a user-side change.