Fix issues when sending images to some clients.

Explanation see here:
https://www.kdab.com/fixing-a-common-antipattern-when-loading-translations-in-qt/

While it does improve performance a bit, it is simply bad for most
distributions, since they don't know and probably don't want to
recompile Nheko. So default it to off. Anyone who wants it can still
toggle it on and it is almost no maintenance cost.