Restrict ScimJacksonXmlBindJsonProvider to only handling SCIMple classes

[bdemers]

Previously application/json requests may have lost any custom extension data.

This change adds applicaiton/json to the list of supproted media types (as recommended by the SCIM specs), but restricts it's types to ONLY classes known by SCIMple, and allows other MessageBodyReader/Writer to handle other requests

Fixes: #390

[bdemers]

@symphony-enrico Can you take a look at this?
I ran a quick test by defining another JacksonXmlBindJsonProvider (bound to */*) with an endpoint that returned a non-SCIMple class (just a hashmap), and that seemed to work well.
(no need to deal with complexities of multiple JAX-RS apps as I previously mentioned 🤞)