uisupport: Let ClickableList inherit from std::vector instead of QList

uisupport: Let ClickableList inherit from std::vector instead of QList

Apparently, a class inheriting from a QList specialization cannot
be properly exported, while this works fine when inheriting from
std::vector instead. Since we now prefer std containers over Qt's
anyway, changing the baseclass is a Good Thing™ either way, so
just do it.