chore: Fix modal nesting, remove react-modal (#1996)

* chore: Fix modal nesting, remove react-modal

* tweak

* fix: Janky route jump when accessing Document -> Move from non-document scene

app/hooks/useUnmount.js

@@ -0,0 +1,16 @@
+// @flow
+import * as React from "react";
+
+const useUnmount = (callback: Function) => {
+  const ref = React.useRef(callback);
+
+  ref.current = callback;
+
+  React.useEffect(() => {
+    return () => {
+      ref.current();
+    };
+  }, []);
+};
+
+export default useUnmount;