Blitz createRenderingEngine(pixelsId) can re-use existing RE
Blitz ._prepareRE doesn't set Pixels if already init. See #10342
Blitz closeRenderingEngines() for cleaning up REs
Webgateway image viewer calls closeRenderingEngines() on close
Blitz RE closed unless image.preventREClose()
webgateway _get_prepared_image() preventREClose() if in request
ome.viewport.js adds 'closeRE=false' to request
Add ?closeRE=false support to render_performance.html
Moved 'close_rendering_engines' url in urls.py to fix merge conflict
Replace image.preventREClose() with reuseREs()

This keeps the creation and closing of REs in sync. We only close an RE if we created it.
webgateway _get_prepared_image() uses img.reuseREs()
Move _reuseREs in Blitz image to fix merge conflict
Refactor PROGRESS_EVENT to improve log output.
merge develop -D org -I include -E conflict -E needs-fixes -E broken: PR 587 (Modulo retrieve (rebased onto develop))
merge develop -D org -I include -E conflict -E needs-fixes -E broken: PR 634 (Big images fs 9701 (develop))
merge develop -D org -I include -E conflict -E needs-fixes -E broken: PR 645 (xsd-fu cleanup)
merge develop -D org -I include -E conflict -E needs-fixes -E broken: PR 654 (Rebased onto develop of spec clean PR)
merge develop -D org -I include -E conflict -E needs-fixes -E broken: PR 655 (Merge xsd-fu changes from schema-2012-06)
merge develop -D org -I include -E conflict -E needs-fixes -E broken: PR 693 (Fs import notifications)
merge develop -D org -I include -E conflict -E needs-fixes -E broken: PR 709 (Cpu develop)