Change the metadata box to be controlled by OpenSeadragon

[tokee]

The metadata-box jumps around when the collage is panned and zoomed. By letting OpenSeadragon control it, it will appear static and in scale with the collage at all times.

[tokee]

There is a problem with this approach: The header and footer of the info-box needs fixed height (but not fixed width) to properly show the text content but OpenSeadragon overlay scaling is all-or-nothing. It might be better to hook into the event system and adjust the overlay after the canvas has been updated.