[Armory Week] User shouldn't be able to scroll when the overlay modal is open
[Armory Week] User shouldn't be able to scroll when the overlay modal is open

finishes https://artsyproduct.atlassian.net/browse/AR-114

cavvia/force-1,anandaroop/force,artsy/force,eessex/force,kanaabe/force,mzikherman/force,yuki24/force,damassi/force,erikdstock/force,erikdstock/force,kanaabe/force,izakp/force,damassi/force,eessex/force,anandaroop/force,artsy/force-public,anandaroop/force,joeyAghion/force,erikdstock/force,xtina-starr/force,izakp/force,damassi/force,anandaroop/force,yuki24/force,erikdstock/force,oxaudo/force,oxaudo/force,yuki24/force,cavvia/force-1,artsy/force,oxaudo/force,damassi/force,yuki24/force,xtina-starr/force,izakp/force,artsy/force-public,cavvia/force-1,eessex/force,oxaudo/force,kanaabe/force,joeyAghion/force,xtina-starr/force,mzikherman/force,cavvia/force-1,joeyAghion/force,kanaabe/force,mzikherman/force,artsy/force,artsy/force,joeyAghion/force,kanaabe/force,eessex/force,izakp/force,mzikherman/force,xtina-starr/force