Changes and Information

Please briefly list the changes (main added features, changed items, or corrected bugs) made:

Set a default for the age group parameters (false).
Fix unit tests and benchmarks by explicitly setting the parameters.
Extend CustomIndexArray to allow for a convenient syntax to set multiple entries to the same value, e.g. parameters.get()[{Agegroup(1), Agegroup(2)}] = true;

Merge Request - Guideline Checklist

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[x] Every addressed issue is linked (use the "Closes #ISSUE" keyword below)
[x] New code adheres to coding guidelines
[x] No large data files have been added (files should in sum not exceed 100 KB, avoid PDFs, Word docs, etc.)
[x] Tests are added for new functionality and a local test run was successful (with and without OpenMP)
[x] Appropriate documentation for new functionality has been added (Doxygen in the code and Markdown files if necessary)
[x] Proper attention to licenses, especially no new third-party software with conflicting license has been added
[ ] (For ABM development) Checked benchmark results and ran and posted a local test above from before and after development to ensure performance is monitored.

[ ] Corresponding issue(s) is/are linked and addressed
[ ] Code is clean of development artifacts (no deactivated or commented code lines, no debugging printouts, etc.)
[ ] Appropriate unit tests have been added, CI passes, code coverage and performance is acceptable (did not decrease)
[ ] No large data files added in the whole history of commits(files should in sum not exceed 100 KB, avoid PDFs, Word docs, etc.)
[ ] On merge, add 2-5 lines with the changes (main added features, changed items, or corrected bugs) to the merge-commit-message. This can be taken from the briefly-list-the-changes above (best case) or the separate commit messages (worst case).

Closes #869