Ui improvements (#4815)

* PLT-4369 - Fixing scroll on mobile in the RHS

* PLT-4924 - Fixing file thumbnail UX

webapp/sass/layout/_sidebar-menu.scss

@@ -1,6 +1,7 @@
 @charset 'UTF-8';
 
 .sidebar--menu {
+    -webkit-overflow-scrolling: touch;
     background: #fafafa;
     border-right: $border-gray;
     display: none;