Fix running without coupling and VTK output in macro-dumux

[IshaanDesai]

This PR fixes the macro-dumux participant in the two-scale heat conduction tutorial in terms of ...

• ... running it without coupling.
• ... output VTK only when the time window has converged. This change requires the adapter function added via Add isTimeWindowComplete API function wrapper dumux-adapter#62.

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.