Proper handling of timezone data on UI. Fixes #301.

Details:
- Date and time handled by OffsetDateTime Java class.
- Track default name with offset (for date local and ISO 8601 options).
- TrackListActivity: shows relative today's date (like Today, Yesterday, 22 Dec, 22 Dec 2021, etc).
- StatisticsRecordedFragment: always shows the original date and time. For example, if you record an activity at 20h then it always will show 20h regardless the zone are where you are.
- Added new tests.

src/main/java/de/dennisguse/opentracks/content/DescriptionGenerator.java

@@ -22,6 +22,8 @@ import android.util.Pair;
 import androidx.annotation.VisibleForTesting;
 
 import java.time.Duration;
+import java.time.OffsetDateTime;
+import java.time.ZoneId;
 
 import de.dennisguse.opentracks.R;
 import de.dennisguse.opentracks.content.data.Distance;
@@ -150,7 +152,7 @@ public class DescriptionGenerator {
         }
 
         // Recorded time
-        builder.append(context.getString(R.string.description_recorded_time, StringUtils.formatDateTime(context, stats.getStartTime())));
+        builder.append(context.getString(R.string.description_recorded_time, StringUtils.formatDateTime(OffsetDateTime.ofInstant(stats.getStartTime(), ZoneId.systemDefault()))));
         builder.append(lineBreak);
 
         return builder.toString();