Cleanup: use ActivityType instead of passing it's id around as String.

Part of #1608.

src/main/java/de/dennisguse/opentracks/ui/aggregatedStatistics/AggregatedStatistics.java

@@ -33,7 +33,7 @@ public class AggregatedStatistics {
 
     @VisibleForTesting
     public void aggregate(@NonNull Track track) {
-        String activityType = track.getActivityType();
+        String activityType = track.getActivityTypeLocalized();
         if (dataMap.containsKey(activityType)) {
             dataMap.get(activityType).add(track.getTrackStatistics());
         } else {

src/main/java/de/dennisguse/opentracks/ui/aggregatedStatistics/AggregatedStatisticsAdapter.java

@@ -184,8 +184,8 @@ public class AggregatedStatisticsAdapter extends BaseAdapter {
         private int getIcon(AggregatedStatistics.AggregatedStatistic aggregatedStatistic) {
             String localizedActivityType = aggregatedStatistic.getActivityType();
             String iconValue = ActivityType.findByLocalizedString(context, localizedActivityType)
-                    .getId();
-            return ActivityType.findByActivityTypeId(iconValue)
+                    .getIconId();
+            return ActivityType.findBy(iconValue)
                     .getIconDrawableId();
         }
     }

src/main/java/de/dennisguse/opentracks/ui/intervals/IntervalsFragment.java

@@ -151,7 +151,7 @@ public class IntervalsFragment extends Fragment {
         ContentProviderUtils contentProviderUtils = new ContentProviderUtils(getContext());
         Track track = contentProviderUtils.getTrack(trackId);
         if (track != null) {
-            isReportSpeed = PreferencesUtils.isReportSpeed(track.getActivityType());
+            isReportSpeed = PreferencesUtils.isReportSpeed(track.getActivityTypeLocalized());
         }
 
         viewModel = new ViewModelProvider(getActivity()).get(IntervalStatisticsModel.class);