Only show "Unlock Widgets" in the UI, not "Lock Widgets"

Summary: Not needed for normal users with the new edit mode system.

Test Plan: Lock the widgets before compiling this patch. Then compile with it, unlock widgets and see that there is no lock option in the panel context menu.

Reviewers: #plasma, #vdg, ngraham, mart

Reviewed By: #plasma, #vdg, ngraham, mart

Subscribers: broulik, mart, ngraham, #vdg, plasma-devel, #plasma

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D24839

containmentactions/contextmenu/menu.cpp

@@ -142,7 +142,9 @@ QList<QAction*> ContextMenu::contextualActions()
                 (c->containmentType() != Plasma::Types::PanelContainment
                  && c->containmentType() != Plasma::Types::CustomPanelContainment)) {
 
-                actions << a;
+                if (name != QLatin1String("lock widgets") || c->corona()->immutability() != Plasma::Types::Mutable) {
+                    actions << a;
+                }
             }
         }
     }