Define new virtual functions Track::GetIntervals (const and non-const)

src/Track.cpp

@@ -1224,6 +1224,16 @@ std::shared_ptr<const Track> Track::SubstituteOriginalTrack() const
    return SharedPointer();
 }
 
+auto Track::GetIntervals() const -> ConstIntervals
+{
+   return {};
+}
+
+auto Track::GetIntervals() -> Intervals
+{
+   return {};
+}
+
 // Serialize, not with tags of its own, but as attributes within a tag.
 void Track::WriteCommonXMLAttributes(
    XMLWriter &xmlFile, bool includeNameAndSelected) const
@@ -1269,6 +1279,8 @@ void Track::AdjustPositions()
    }
 }
 
+TrackIntervalData::~TrackIntervalData() = default;
+
 bool TrackList::HasPendingTracks() const
 {
    if ( !mPendingUpdates.empty() )