CI build failure for Vaadin 23 and 24

After adding CI build checks for Vaadin 23 and 24 (588662e, 8678051, 676ed67) I found that 23 and 24 builds fail because of the removal of HtmlImport, which is used here

CarouselAddon/src/main/java/com/flowingcode/vaadin/addons/carousel/Carousel.java

Line 36 in 588662e

@HtmlImport("bower_components/l2t-paper-slider/l2t-paper-slider.html")

The add-on, however, IS compatible with Vaadin 23 and 24 because missing annotations do not throw any exception (see https://stackoverflow.com/q/3567413/1297272). We have demos at https://addonsv23.flowingcode.com/carousel and https://addonsv24.flowingcode.com/carousel

I think we should revert the mentioned commits, and keep CI for Vaadin 14 only.

I agree. Let's do that. If we have issues later we can just remove the annotation and stop supporting Vaadin versions < 14