Set JSON as a default content type

[gorbunkov]

In rest dispatcher spring xml the content negotiation manager bean must e defined with a default content type application/json:

    <bean id="contentNegotiationManager"
          class="org.springframework.web.accept.ContentNegotiationManagerFactoryBean">
        <property name="defaultContentType" value="application/json"/>
    </bean>

    <mvc:annotation-driven content-negotiation-manager="contentNegotiationManager" />

Forum topic: https://www.cuba-platform.com/discuss/t/how-to-set-default-output-to-json-for-rest/10089