org.kde.plasma:force-create in Containment

so much for removing sytray-related hacks.. :/
when the widgets are locked, must be possible to add/remove
widgets in the sytemtray anyways, as their creation/destruction
can depend from dbus activation (or the first time you launch
plasma with the new systray and it must be populated)

Change-Id: I8095ebf831ae57e1306a4d623b253c2a10ef219f
REVIEW:127373

src/plasma/private/containment_p.cpp

@@ -195,7 +195,7 @@ Applet *ContainmentPrivate::createApplet(const QString &name, const QVariantList
         return 0;
     }
 
-    if (q->immutability() != Types::Mutable) {
+    if (q->immutability() != Types::Mutable && !args.contains("org.kde.plasma:force-create")) {
 #ifndef NDEBUG
         // qCDebug(LOG_PLASMA) << "addApplet for" << name << "requested, but we're currently immutable!";
 #endif