Fix min required libaccounts-qt version
libaccounts-qt 1.15 uses deprecated Qt API in its headers (QString::null), which to support again would mean much work.
https://gitlab.com/accounts-sso/libaccounts-qt/-/blob/VERSION_1.15/Accounts/account.h
vs.
https://gitlab.com/accounts-sso/libaccounts-qt/-/blob/VERSION_1.16/Accounts/account.h
1.16 as working version is > 2 years old and should be available in all target distributions of Gear 21.12
See
- https://repology.org/project/libaccounts-qt5/versions
- https://repology.org/project/libaccounts-qt/versions
@aacid @heikobecker Would be an exception from the dependency freeze, so asking for your comment as well.