Generate UUID for each track (necessary for synchronization).

Fixes #294.

src/androidTest/java/de/dennisguse/opentracks/util/UUIDUtilsTest.java

@@ -0,0 +1,23 @@
+package de.dennisguse.opentracks.util;
+
+import androidx.test.ext.junit.runners.AndroidJUnit4;
+
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import java.util.UUID;
+
+@RunWith(AndroidJUnit4.class)
+public class UUIDUtilsTest {
+
+    @Test
+    public void test() {
+        UUID uuid = UUID.randomUUID();
+
+        byte[] bytes = UUIDUtils.toBytes(uuid);
+        UUID output = UUIDUtils.fromBytes(bytes);
+
+        Assert.assertEquals(uuid, output);
+    }
+}