New CountVisitor to count the number of sources in session

Session size is the number of elements, use CountVisitor to count the total number of sources inside (recursively through SessionSources).

Session.cpp

@@ -33,6 +33,7 @@
 #include "MixingGroup.h"
 #include "ControlManager.h"
 #include "SourceCallback.h"
+#include "CountVisitor.h"
 #include "Log.h"
 
 #include "Session.h"
@@ -432,11 +433,21 @@ SourceList Session::getDepthSortedList() const
     return depth_sorted(sources_);
 }
 
-uint Session::numSource() const
+uint Session::size() const
 {
     return sources_.size();
 }
 
+uint Session::numSources() const
+{
+    CountVisitor counter;
+    for( SourceList::const_iterator it = sources_.cbegin(); it != sources_.cend(); ++it) {
+        (*it)->accept(counter);
+    }
+    return counter.numSources();
+}
+
+
 SourceIdList Session::getIdList() const
 {
     return ids(sources_);