Implementation of user defined mixing deactivation limit

Mixing view handles to grab and scale limbo area. Saving of user defined limit in Session (and snapshot). Testing for source activation outside of update during session update loop.

ActionManager.cpp

@@ -69,6 +69,9 @@ void captureMixerSession(tinyxml2::XMLDocument *doc, std::string node, std::stri
         delete thumbnail;
     }
 
+    // save session attributes
+    sessionNode->SetAttribute("activationThreshold", se->activationThreshold());
+
     // save all sources using source visitor
     SessionVisitor sv(doc, sessionNode);
     for (auto iter = se->begin(); iter != se->end(); ++iter, sv.setRoot(sessionNode) )