chore: Flatten left nav in preparation to refactor drag to reorder (#1689)

* flatten hierarchy
* fix drop to import positioning on collections

app/components/Sidebar/components/Collections.js

@@ -61,7 +61,6 @@ class Collections extends React.Component<Props> {
         {collections.orderedData.map((collection) => (
           <CollectionLink
             key={collection.id}
-            documents={documents}
             collection={collection}
             activeDocument={documents.active}
             prefetchDocument={documents.prefetchDocument}