Add Compound Documents integration tests

We want to rework the existing tests and add integration tests using the REST API instead as this is what the UI will use later on.

Tests we want:

1/ Create a CompoundDocument doc in a given folder and validate that the created compound document has:

• the CompoundDocument facet
• File, Audio, Picture, Video and CompoundDocumentFolder as subtypes.

2/ Test that all subtypes can be created in a given CompoundDocument doc.

3/ Test that a CompoundDocumentFolder doc has File, Audio, Picture, Video and CompoundDocumentFolder as subtypes.

4/ Test that a Folder cannot be created inside a CompoundDocument or CompoundDocumentFolder doc.