Add ability to fetch Google Doc API from extension

We ought to be able to fetch information about a given Google Document from the extension via the Google Docs API.

This is possible to do; however, we need to add a few permission related settings to the extension's `manifest.json` file. We need to add an `oauth2` section to the manifest detailing our `client_id` (from the Google API portal) and the scopes we wish to use (`https://www.googleapis.com/auth/documents.readonly`).

Once this is added, we should be able to call `chrome.identity.getAuthToken()` to fetch the user's OAuth token and include it in our headers when we query the Google Docs API for a specific document.

If data about a given document is successfully received, we should send it back to Learning Observer. The returned data will be in [this structure](https://developers.google.com/docs/api/reference/rest/v1/documents#Document).

Start with the extension's manifest.json and the planned chrome.identity.getAuthToken() call; compare the requested scope and API response with the linked Google Docs Document structure. Done means a given document can be queried with the OAuth token and the returned data is sent back to Learning Observer.

Written by the indexing model from the issue text.