Loading state

[stephenwf]

When a page decides to render a canvas panel it may have some information that would make the loading quicker - like a thumbnail or similar. We should support this in the canvas panel and image service components, and replace the loading spinner with something that fits the same size as the final loaded image to avoid layouts switching

Progressive states

• loading with nothing at all to show yet
• still loading but have a fuzzy thumb for you
• ready, fully loaded

These could also be emitted as events, so that the containing page can also respond to them.