Webatrice: Update nav (#4380)

* wip: subnav debug

* nav redesign

* remove unnecessary code

* remove subnav

* add leaveRoom button

Co-authored-by: Jeremy Letto <jeremy.letto@datasite.com>

webclient/src/components/ThreePaneLayout/ThreePaneLayout.css

@@ -26,9 +26,11 @@
   height: 100%;
   width: 100%;
   flex-shrink: 1;
+  overflow: hidden;
 }
 
 .three-pane-layout .grid-main__top.fixedHeight,
 .three-pane-layout .grid-main__bottom.fixedHeight {
   height: 50%;
+  overflow: visible;
 }