Move document improvements (#927)

* Show all collections in UI

* Introduce command pattern

* Actually remove from previous collection

* Stash

* Fixes: Promises resolved outside of response lifecycle

* 💚

* 💚

* documentMover tests

* Transaction

* Perf. More in transactions

app/stores/BaseStore.js

@@ -65,6 +65,10 @@ export default class BaseStore<T: BaseModel> {
     return this.create(params);
   }
 
+  get(id: string): ?T {
+    return this.data.get(id);
+  }
+
   @action
   async create(params: Object) {
     if (!this.actions.includes('create')) {