Support 'PATCH /resources/<id>?preferred_handler=<PHP|Ruby>'

[zanerock]

Allow configuration of service handlers to prefer one type. We support batch PATH:

PATCH /resources?default_handler=<PHP|Ruby>

and item handler:

• PATCH /resources/<item ID>/<cardnality>/<GET|POST|PUT|PATCH|DELETE<?preferred-format=<PHP|RUBY>

Relate to: #6