Add methods used by Plasma::Containment *ShellCorona::addPanel(const QString &plugin) (see plasma-workspace: https://phabricator.kde.org/D10344 ):
Containment *createContainmentForScreen(int screenNum, const QString &name, const QVariantList &args = QVariantList());
Containment *addContainmentForScreen(int screenNum, const QString &name, const QVariantList &args, uint id, bool delayedInit = false);
void Containment::setLastScreen(int screen);

These are needed to create panels on the current screen in multi-monitor environments, so panels can be created on all desired screens.

Currently it is only possible to have panels on one screen.

More than one monitor connected: Right-click on empty desktop, "Add Panel", choose any ("Empty", "Standard",...). Panel appears on monitor where you opened the context menu.