Redo marker selection code

app/timeline/timelinemarker.cpp

@@ -66,6 +66,18 @@ void TimelineMarker::set_color(int c)
   emit ColorChanged(color_);
 }
 
+bool TimelineMarker::active()
+{
+  return active_;
+}
+
+void TimelineMarker::set_active(bool active)
+{
+    active_ = active;
+
+    emit ActiveChanged(active_);
+}
+
 void TimelineMarkerList::Save(QXmlStreamWriter *writer) const
 {
   foreach (TimelineMarker* marker, markers_) {

app/timeline/timelinemarker.h

@@ -44,6 +44,9 @@ public:
   int color();
   void set_color(int c);
 
+  bool active();
+  void set_active(bool active);
+
 signals:
   void TimeChanged(const TimeRange& time);
 
@@ -51,6 +54,8 @@ signals:
 
   void ColorChanged(int c);
 
+  void ActiveChanged(bool active);
+
 private:
   TimeRange time_;
 
@@ -58,6 +63,8 @@ private:
 
   int color_;
 
+  bool active_;
+
 };
 
 class TimelineMarkerList : public QObject