Add image to a presentation from a URL/URI

The ability to use URI based images allows us to easily update branding and styles without updating each presentation. HAving the same refresh options as Aha views such as manual or automatic refresh gives us some control.

This is also necessary when bringing content from external sources. They can export as an image or provide a URI to load the content directly.

There is authentication considerations i imagine, perhaps an unauthenticated URI as an initial implementation, allowing user to evaluate the capablity and decide if its safe enough or if further implementation is required.