AUI-1402 Postpone node render phase using 'lazyLoad' attribute.

Hey Peter,

We had some issues some time ago with the performance of the tree in IE. So I came up with this ``lazyLoad`` attribute. The idea is to postpone processing as much as we can. I've made some changes to make ``_createFromHTMLMarkup`` take advantage of ``lazyLoad``. Can you test it and give me some feedback?

Thanks!