Import: re-implement KML parsing.

Fixes #790.

src/main/java/de/dennisguse/opentracks/content/data/Track.java

@@ -33,6 +33,7 @@ import de.dennisguse.opentracks.stats.TrackStatistics;
  * @author Leif Hendrik Wilden
  * @author Rodrigo Damazio
  */
+//TODO Do not default initialize attributes; might be confusing for debugging
 public class Track {
 
     private Track.Id id;