WIP: RestAPI unit-tests placeholders

Work in progress, test driven development and unit-tests for #480. The tests are failing because there is no implementation, yet. Do not merge into `master` branch.

Run tests via:
```bash
python setup.py test -s invenio.b2share.testsuite.test_b2deposit_restapi
```
you need to use [`lazy_import`](https://github.com/inveniosoftware/invenio/blob/pu/invenio/base/wrappers.py#L128) or import `oauth2` inside a test case (application context).