Add Fixtures for unit tests

Summary:
Add some fixtures for the unit tests.
This also contains Request/Response fixtures for the browser binding based on
the official cmis specification:
https://tools.oasis-open.org/version-control/browse/wsvn/cmis/trunk/cmis-v1.1/examples/browser/#_trunk_cmis-v1.1_examples_browser_

Reviewers: #forgetit-dev, claus.due

Reviewed By: #forgetit-dev, claus.due

Differential Revision: https://phabricator.dkd.de/D422