switch to OpenSeadragon

[#67574772]
only ignore static files at the top level, not inside apps
update openseadragon js with locally built copy that is namespace-aware
move single and multi-page mode toggle buttons below the line for consistency with collection/search
enable seadragon navigator; custom zoom toolbar with bootstrap buttons

[#67574772]
fix logic for toggling deep zoom mode; reset zoom on exit

[#67574772]