Added REST functional tests

Those tests are written for http://jira.ez.no/browse/ezp-21018, and are meant to consolidate the current refactoring of the remaining RMF API elements.

They roughly test every feature according to the specs and current implementation, through HTTP calls to the REST server.

The HTTP calls are far from ideal, and we should ideally switch to WebTestCase (impl-EZP-21018-rest_functional_tests), but the result is pretty much the same.

In their current shape *the tests directly affect the database and don't use any kind of fixture*. This also needs to be improved, but gets the testing done in the meantime.

# Configuration

The tests rely on two environnement variables, EZP_TEST_REST_HOST and EZP_TEST_REST_HOST.

# Running the tests

ezpublish-kernel$ phpunit eZ/Publish/Core/REST/Server/Functional