import & adapt dyndzi/deepzoom logic from readux v1

[#67574772]
preliminary, rough integration of deep zoom onto page view (needs rework)

[#67574772]
add deepzoom static js content
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]
updated copy of openseadragon, with dzi namespace support in firefox
updated copy of openseadragon, with dzi namespace support in firefox (fix typo)
clean up deepzoom js; disable zoom if page image errors

[#67574772]
Merge branch 'develop' into feature/deepzoom

Conflicts:
	pip-install-req.txt
update collection list test so it tests the correct url
tweak wording so collection cover and list views are more consistent
Merge branch 'feature/deepzoom' into develop