Export: disable "export all tracks into one file"-functionality as markers cannot be correctly restored (KML/KMZ).

Part of #2383.

src/main/java/de/dennisguse/opentracks/io/file/exporter/KMLTrackExporter.java

@@ -49,6 +49,8 @@ import de.dennisguse.opentracks.util.StringUtils;
  * Convert {@link Track} incl. {@link Marker} and {@link TrackPoint} to KML version 2.3.
  * <a href="https://docs.opengeospatial.org/is/12-007r2/12-007r2.html">...</a>
  *
+ * WARNING: exporting multiple tracks (each with markers) into one file, will not allow to restore to which track a marker belonged.
+ *
  * @author Sandor Dornbush
  * @author Rodrigo Damazio
  * @author Leif Hendrik Wilden

src/main/res/xml/settings_import_export.xml

@@ -24,12 +24,13 @@
                 android:targetClass="de.dennisguse.opentracks.io.file.importer.DirectoryChooserActivity$ExportDirectoryChooserActivity"
                 android:targetPackage="@string/applicationId" />
         </Preference>
-        <Preference
-            android:title="@string/menu_export_all_one_file">
-            <intent
-                android:targetClass="de.dennisguse.opentracks.io.file.importer.DirectoryChooserActivity$ExportDirectoryChooserOneFileActivity"
-                android:targetPackage="@string/applicationId" />
-        </Preference>
+<!-- Disabled as the used structure for KML/KMZ does not allow assigning markers correctly on import. -->
+<!--        <Preference-->
+<!--            android:title="@string/menu_export_all_one_file">-->
+<!--            <intent-->
+<!--                android:targetClass="de.dennisguse.opentracks.io.file.importer.DirectoryChooserActivity$ExportDirectoryChooserOneFileActivity"-->
+<!--                android:targetPackage="@string/applicationId" />-->
+<!--        </Preference>-->
         <Preference
             android:key="@string/settings_default_export_directory_key"
             android:title="@string/settings_default_export_uri_title">