fix: Separate toasts storage to own MobX store (#2339)

Co-authored-by: Tom Moor <tom.moor@gmail.com>

app/hooks/useToasts.js

@@ -0,0 +1,8 @@
+// @flow
+import useStores from "./useStores";
+
+export default function useToasts() {
+  const { toasts } = useStores();
+
+  return { showToast: toasts.showToast, hideToast: toasts.hideToast };
+}