Integrated Coinbase support (closes #708)

Squashed commit of the following:

commit e6547225c8e9a87765bf0e4e5a19bb32f2be3f47
Author: Raymond Penners <raymond.penners@intenct.nl>
Date:   Mon Sep 15 20:37:18 2014 +0200

    Integrated Coinbase support

commit d1eee95c71ca3f1095c67ee03610611bf8cd5ad4
Author: Josh Owen <josh@openfolio.com>
Date:   Fri Sep 5 20:28:11 2014 -0400

    use full test response

commit f44b78e18a391850d37c46f925a0d770c657ef05
Author: Josh Owen <josh@openfolio.com>
Date:   Fri Sep 5 20:25:40 2014 -0400

    fix coinbase test

commit 00a706c5c06ef63e68f83be119cf086b898ac718
Author: Josh Owen <josh@openfolio.com>
Date:   Fri Sep 5 19:02:10 2014 -0400

    use requests.get

commit 80a821c265ec95d8890c624e174ebab6cf015c71
Author: Josh Owen <josh@openfolio.com>
Date:   Fri Sep 5 16:08:28 2014 -0400

    test coinbase

commit bb7adab0c3e42f5b503c723126057696f325ed26
Author: Josh Owen <josh@openfolio.com>
Date:   Fri Sep 5 16:04:44 2014 -0400

    set default scope

commit 7a425a6294ae5c9cab4fdf4ad2afece57f7ce24b
Author: Josh Owen <josh@openfolio.com>
Date:   Fri Sep 5 15:50:24 2014 -0400

    first stab at coinbase integration