Add hash comparison to the has_changed() function

[bernd-wechner]

Degoo metadata does not include a remote hash. We can calculate one locally of course. But there is a good chance we can coax one out of the backed Google File Store that Degoo are using:

Here's a place to start reading:

https://stackoverflow.com/questions/25234515/how-to-get-the-md5-of-an-object-that-has-already-been-stored