title: Using the UIDocumentPickerViewController, is it possible to show a default service (Dropbox, Google Drive, etc) on first open like in Slack?
body: <p>Normally, the behavior with UIDocumentPicker is that you present, then the user must use the "Locations" menu on the top right to switch between the services. Is it possible to display either "Dropbox" or "Google Drive" first by default? Almost as if we're "deeplinking" into the UIDocumentPicker service.</p>
  
  <p>It seems like Slack App is able to do this and also the MyMail App but I wasn't able to find an API for it. Any ideas?</p>
  
  <p><img src="https://i.stack.imgur.com/CQCwr.png" alt="Slack App"></p>