Context: Print Thin Walls and Fill Perimeter Gaps are old settings that aren't needed any more since we switched to libArachne (Varianble Line Widths).
CURA-7148
Although it is not entirely sure yet, we are fairly certain that libArachne release will have
a setting version of 18, so it is changed by this commit. With this change, the VersionUpgrader
will be properly triggered.
Contributes to CURA-7683 and CURA-7656