OLTU-125 - Create a 'commons' module for JSON reader/writer

added small commons 'json' and 'encodedtoken' modules in order to drop duplicate codes in JWT/JWS modules

git-svn-id: https://svn.apache.org/repos/asf/oltu/trunk@1536690 13f79535-47bb-0310-9956-ffa450edef68