Network requests on each render

Hi! Thanks for the module.

I have an example here: http://requirebin.com/?gist=f2a99cc27c465ed51eb8159830836ca4. In it, each time I call `update` and `bel` creates a new element, a local network request is made for the base64 inlined image, even though it did not change.

Should this be happening? I guess it makes sense, new element is created, `bel` is fetching it’s content. But that results in a poor performance — when I add a relatively large image, like 3mb, the Chrome browser tab can barely function and the interface becomes unusable.

To reproduce: navigate to http://uppy.io/examples/modal/index.html, click “open modal” and drag two files to the dragdrop area. Open network tab, click “upload”.

What am I doing wrong? Thank you!

Start by reproducing the behavior in the linked requirebin example and the uppy.io modal example, watching the browser network tab while calling update and using bel with an inlined image. Trace how new elements and unchanged base64 image content are handled, then verify that repeated updates no longer trigger unnecessary requests and that the upload interface remains usable.

Written by the indexing model from the issue text.