Add Lazyload option to Image Block options

While lazy loading is in general a good thing, you often want to load the first contentful paint normally. To avoid having to write JS to achieve this, this could be done with a simple checkbox option labelled "Lazy Load" in the Block Options for the Image Block, which is checked by default. Giving the option to uncheck this to avoid lazy loading FCP resources will make it easier to gain high Pagespeed-scores.