@Override public String getUserAgentStylesheet() {
        if (null == userAgentStyleSheet) { userAgentStyleSheet = getClass().getResource("tilesfx.css").toExternalForm(); }
        return userAgentStyleSheet;
    }
Calling this method will stop all threads. This is needed when using
JavaFX on mobile devices when the device goes to sleep mode.
src/main/java/eu/hansolo/tilesfx/Tile.java