Support file shortcuts

[douglasward]

Problem Description

I would like to include documents in various places in the documentation library as the same information is relevant for various areas. In google drive this can be done by creating file shortcuts but these are not yet supported by this library.

Library does not support viewing shortcuts yet.

Feature

Implement the support for shortcuts as it should be very similar to normal documents.

[jpmckinney]

As of September 30, Google Drive creates shortcuts waayyyyyy more frequently (it's no longer possible to file a document in multiple locations, which is pretty much 100% of the time if you aren't the file's owner), so support for shortcuts is pretty important. Right now they open as external links.