Documentation - Provide API request/response samples in JSON

[cdanger]

Currently, there are only examples for Content-Type/Accept = application/xml in doc. Provide some for Content-Type/Accept = application/json
Plenty of raw examples in the test suite output to take from (that you can get by running maven test in webapp module after changing log level to INFO for logger org.apache.cxf in src/test/resources/authzforce-ce-server/conf/logback.xml):

TestSuite-output.txt

It is not yet certain that it is worth the trouble because:

1. On PAP API, the JSON format has serious limitations compared to XACML/XML.
2. For the PDP API, the JSON format (for XACML Requests/Responses) is the one already fully specified in this XACML standard: JSON Profile of XACML 3.0 Version 1.1. So please refer to it.