Add a next/prev shortcut (F6 for now) for outputpanes.

This one has some magic inside to always use the current outputpane.
This solves the issue that I don't want Search and Build Issues list to
have its own set of next/prev shortcuts. todo is a better definition of
next for the build issues and/or a way to restrict it only to errors.

src/plugins/coreplugin/messageoutputwindow.cpp

@@ -89,3 +89,28 @@ int MessageOutputWindow::priorityInStatusBar() const
 {
     return -1;
 }
+
+bool MessageOutputWindow::canNext()
+{
+    return false;
+}
+
+bool MessageOutputWindow::canPrevious()
+{
+    return false;
+}
+
+void MessageOutputWindow::goToNext()
+{
+
+}
+
+void MessageOutputWindow::goToPrev()
+{
+
+}
+
+bool MessageOutputWindow::canNavigate()
+{
+    return false;
+}