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/core.h

@@ -26,6 +26,7 @@
 #include <QTimer>
 
 #include "common/rational.h"
+#include "common/timecodefunctions.h"
 #include "project/item/footage/footage.h"
 #include "project/item/sequence/sequence.h"
 #include "project/project.h"
@@ -125,6 +126,16 @@ public:
   ProjectViewModel* GetActiveProjectModel();
   Folder* GetSelectedFolderInActiveProject();
 
+  /**
+   * @brief Gets current timecode display mode
+   */
+  Timecode::Display GetTimecodeDisplay() const;
+
+  /**
+   * @brief Sets current timecode display mode
+   */
+  void SetTimecodeDisplay(Timecode::Display d);
+
   /**
    * @brief Sets state to "modified" so that the GUI will prompt the user to save before closing
    *
@@ -269,6 +280,11 @@ signals:
    */
   void SnappingChanged(const bool& b);
 
+  /**
+   * @brief Signal emitted when the default timecode display mode changed
+   */
+  void TimecodeDisplayChanged(Timecode::Display d);
+
 private:
   /**
    * @brief Get the file filter than can be used with QFileDialog to open and save compatible projects