Moved forward declaration of perf_data_viewer_widget in application.hpp to qpvt namespace.

pv_app/src/application.hpp

@@ -33,9 +33,11 @@
 
 class QSplitter;
 
-namespace pv_app {
+namespace qpvt {
+  class perf_data_viewer_widget;
+}
 
-class perf_data_viewer_widget;
+namespace pv_app {
 
 //------------------------------------------------------------------------------
 class application