Merge branch 'maint-2.0' into maint-2.1
- maint-2.0: installation: more dependency pinning installation: upper limit on Flask-Babel installation: fix prerequisite package versions iiif: set default cache handler properly global: new blocks for the header template global: mustache templates as text/html records: JavaScript refactoring and bug fixing records: bundle file size reduction records: removal of cloudconnector modal cloudconnector: onedrive icon image global: libraries can be loaded from their CDN installation: fix entry_points for pip7 search: intbitset could be None