JP Image Widget hanging /wp-admin dashboard Widget page

The JP Image Widget can potentially hang the /wp-admin dashboard Widget page if the source URLs are tardy enough and/or there are a lot of image widgets on the page.

Shared hosts in particular have strict request timeouts and when the conditions are right the Image Widget appears to have notable potential to overrun them. I think we should err on the side of a low timeout since the code looks to be for optimizing browser layout and it seems to work fine even if we don't have dimensions ahead of time.