core: added signalling for timecode display changes

Allows targeted application-wide UI updates for when the user changes the
timecode display so that the response is immediate.

app/widget/slider/timeslider.cpp

@@ -1,11 +1,14 @@
 #include "timeslider.h"
 
 #include "common/timecodefunctions.h"
+#include "core.h"
 
 TimeSlider::TimeSlider(QWidget *parent) :
   IntegerSlider(parent)
 {
   SetMinimum(0);
+
+  connect(Core::instance(), &Core::TimecodeDisplayChanged, this, &TimeSlider::TimecodeDisplayChanged);
 }
 
 void TimeSlider::SetTimebase(const rational &timebase)
@@ -25,10 +28,15 @@ QString TimeSlider::ValueToString(const QVariant &v)
 
   return Timecode::timestamp_to_timecode(v.toLongLong(),
                                          timebase_,
-                                         Timecode::CurrentDisplay());
+                                         Core::instance()->GetTimecodeDisplay());
 }
 
 QVariant TimeSlider::StringToValue(const QString &s, bool *ok)
 {
-  return QVariant::fromValue(Timecode::timecode_to_timestamp(s, timebase_, Timecode::CurrentDisplay(), ok));
+  return QVariant::fromValue(Timecode::timecode_to_timestamp(s, timebase_, Core::instance()->GetTimecodeDisplay(), ok));
+}
+
+void TimeSlider::TimecodeDisplayChanged()
+{
+  UpdateLabel(Value());
 }