s/emty/empty/g.

Port away from most cases of Q_FOREACH to C++11 ranged for loop.

In order to avoid deep copies, Qt containers over which we iterate must be const
The remaining unported cases require qAsConst (Qt 5.7) or std::as_const (C++17)

This fixes CAL-385 #close

displaymanager: write processed DM list to globalstorage

This is disabled by default. To enable, provide a geoipUrl setting in
locale.conf.
Relies on the RequirementsChecker output, in the welcome module.