fix: Keyboard accessible context menus (#1768)

- Makes menus fully accessible and keyboard driven
- Currently adds 2.8% to initial bundle size due to the inclusion of Reakit and its dependency, popperjs.
- Converts all menus to functional components
- Remove old custom menu system
- Various layout and flow improvements around the menus

closes #1766

app/components/Toasts/components/Toast.js

@@ -8,7 +8,7 @@ import type { Toast as TToast } from "types";
 
 type Props = {
   onRequestClose: () => void,
-  closeAfterMs: number,
+  closeAfterMs?: number,
   toast: TToast,
 };