Setting an escaped URL in a model fails

This PR contains a failing test when setting an escaped url in a model, eg:

`my_model.image_url = 'http://foo.bar/not%20working.jpg'`

I believe this is a bug as setting a non-escaped url also fails (it raises an `InvalidURI` error):

`my_model.image_url = 'http://foo.bar/not working.jpg'`

I'll try to go further soon