Support `crossorigin` attribute

[giggio]

When creating the preload element the crossorigin attribute is added to it, but it is not added to the link element that is added to the end of the document.

This makes the preload not be used, Chrome creates a warning like this:

A preload for '<URL>' is found, but is not used because the request credentials mode does not match. Consider taking a look at crossorigin attribute.

So, the preload tag should include it if it exists.