private static ContentResolver getContentResolver() {
        return CgeoApplication.getInstance().getContentResolver();
    }
Calculates a xml theme name fit for user display (in dropdown etc)

@param file    theme file name
@param zipPath if theme file is a ZIP, then this contains the zip-internal path to the xml. Otherwise null
@return user display theme name
main/src/main/java/cgeo/geocaching/unifiedmap/mapsforgevtm/MapsforgeThemeHelper.java