feature request - loading timeout

[burczu]

First of all thanks for very useful component! I use it in my project and sometimes notice that the browser waits for a long time to load the primary image. Of course it loads a fallback image after all but I think it would be nice to have an additional attribute, e.g. loadingTimeout, which would allow us to limit the loading time of the primary image. If the timeout exceed it would just show the fallback image. Does it make any sense?