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/androidTest/java/de/dennisguse/opentracks/content/DescriptionGeneratorTest.java

@@ -27,6 +27,8 @@ import org.junit.runner.RunWith;
 
 import java.time.Duration;
 import java.time.Instant;
+import java.time.OffsetDateTime;
+import java.time.ZoneId;
 
 import de.dennisguse.opentracks.R;
 import de.dennisguse.opentracks.content.data.Distance;
@@ -91,7 +93,7 @@ public class DescriptionGeneratorTest {
                 + "Min elevation: -500 m (-1640 ft)<br>"
                 + "Elevation gain: 6000 m (19685 ft)<br>"
                 + "Elevation loss: 6000 m (19685 ft)<br>"
-                + "Recorded: " + StringUtils.formatDateTime(context, START_TIME) + "<br>";
+                + "Recorded: " + StringUtils.formatDateTime(OffsetDateTime.ofInstant(START_TIME, ZoneId.systemDefault())) + "<br>";
 
         assertEquals(expected, descriptionGenerator.generateTrackDescription(track, true));
     }
@@ -127,7 +129,7 @@ public class DescriptionGeneratorTest {
                         + "Fastest pace: 0:10 min/km (0:16 min/mi)<br>"
                         + "Elevation gain: 6000 m (19685 ft)<br>"
                         + "Elevation loss: 6000 m (19685 ft)<br>"
-                        + "Recorded: " + StringUtils.formatDateTime(context, START_TIME) + "<br>";
+                        + "Recorded: " + StringUtils.formatDateTime(OffsetDateTime.ofInstant(START_TIME, ZoneId.systemDefault())) + "<br>";
 
         assertEquals(expected, descriptionGenerator.generateTrackDescription(track, true));
     }