Allowing to override plasma mutability setting on containment creation

This adds a 'Sledge Hammer'-like flag (trust me I know what I'm doing)
for creating the containment even if the plasma is not set on
'mutable'.

src/plasma/corona.cpp

@@ -241,7 +241,7 @@ KSharedConfigPtr Corona::config() const
 
 Containment *Corona::createContainment(const QString &name, const QVariantList &args)
 {
-    if (d->immutability == Types::Mutable) {
+    if (d->immutability == Types::Mutable || args.contains("org.kde.plasma:force-create")) {
         return d->addContainment(name, args, 0);
     }