Isolate REST API module

Try to isolate the API module in its own host to avoid getting all the writers/readers contributed to other modules/applications in the REST API itself.

This leads to errors when reader such as JacksonJsonProvider passes before JsonCoreIODelegate to read a document. See NCO-1307.

To isolate, we should add host=api in the Nuxeo-WebModule definition. As the writers/readers will be isolated, we will probably need to add required writers/readers to APIModule.