Ref T301, application contexts pings (by re-registering) identifiers again. By that it can be detected if the GUI is crashed

* ping timer in proxy
* utility function in timestamp list
* adjusted UI component displaying identifiers in core

src/blackmisc/timestampobjectlist.cpp

@@ -111,6 +111,12 @@ namespace BlackMisc
         });
     }
 
+    template<class OBJ, class CONTAINER>
+    CONTAINER ITimestampObjectList<OBJ, CONTAINER>::findAfterNowMinusOffset(qint64 msOffset) const
+    {
+        return this->findAfter(QDateTime::currentMSecsSinceEpoch() - msOffset);
+    }
+
     template<class OBJ, class CONTAINER>
     OBJ ITimestampObjectList<OBJ, CONTAINER>::findObjectAfterOrDefault(qint64 msSinceEpoch) const
     {

src/blackmisc/timestampobjectlist.h

@@ -72,6 +72,9 @@ namespace BlackMisc
         //! List of objects after msSinceEpoch (newer)
         CONTAINER findAfter(qint64 msSinceEpoch) const;
 
+        //! List of objects before now - offset
+        CONTAINER findAfterNowMinusOffset(qint64 msOffset) const;
+
         //! List of objects after msSinceEpoch (newer)
         OBJ findObjectAfterOrDefault(qint64 msSinceEpoch) const;