unify JSON libraries

[Robert Jäschke]

Currently, different modules use different JSON libraries (check with grep json **/pom.xml):

• net.sf.json: json-lib
• org.json: json
• com.googlecode.json: json-simple

In the meantime, there's JSR 353 for JSON Processing with Java, which also includes a JSON lib.

Please unify the JSON handling in BibSonomy by reducing the redundancy to JSON libraries.