Entire cleanup of ActionManager

History of previous id of sources is now obtained in SessionLoader; no
need to store the id of the source in action manager XML (so also
removed in View current id).

ActionManager.h

@@ -22,7 +22,7 @@ public:
         return _instance;
     }
 
-    void store(const std::string &label, uint64_t id = 0);
+    void store(const std::string &label);
 
     void clear();
     void undo();