Disallow keyboard focus in sidebar

Makes keyboard shortcuts from the split VC's primary content available

See #302

Tusker/Screens/Main/MainSidebarViewController.swift

@@ -89,6 +89,8 @@ class MainSidebarViewController: UIViewController {
         collectionView.delegate = self
         collectionView.dragDelegate = self
         collectionView.isSpringLoaded = true
+        // TODO: allow focusing sidebar once there's a workaround for keyboard shortcuts from main split content not being accessible when not in the responder chain
+        collectionView.allowsFocus = false
         view.addSubview(collectionView)
         
         dataSource = createDataSource()