private static String[] getLegacyPreferenceKeysFor(final int keyId) {
        if (keyId == R.string.pref_persistablefolder_offlinemaps) {
            return new String[]{"mapDirectory"};
        } else if (keyId == R.string.pref_persistablefolder_gpx) {
            return new String[]{"gpxExportDir", "gpxImportDir"};
        } else if (keyId == R.string.pref_persistablefolder_offlinemapthemes) {
            return new String[]{"renderthemepath"};
        } else {
            return new String[0];
        }
    }
gets current setting for a persistable uri or null if unset
should be called by BackupUtils.restoreInternal only
main/src/main/java/cgeo/geocaching/settings/Settings.java