Hide scrollbars on <html> tag when KModal is open
Hide scrollbars on <html> tag when KModal is open

Fixes #6212

mrpau/kolibri,indirectlylit/kolibri,learningequality/kolibri,indirectlylit/kolibri,learningequality/kolibri,mrpau/kolibri,indirectlylit/kolibri,learningequality/kolibri,learningequality/kolibri,indirectlylit/kolibri,mrpau/kolibri,mrpau/kolibri