Allow extension to see files and folders which already exist on Drive

[GustavoASC]

Overview

The extension currently uses drive.file scope, so it can only access files and folders uploaded to Google Drive through this extension itself. Some people are willing to manage other files through this extension but it's not currently possible.

The files manually uploaded to Google Drive through the Drive website, for example, do not appear on this extension.

Suggestion

Use Google Picker API, so we can provide access to specific files which have been manually uploaded through Drive website or uploaded through other applications;

Google Picker API would show a dialog like the one below, so after selecting files/folders with Google Picker API, they would appear on the extension Tree View (at least I believe this would be the behavior of Picker API).