Repairing SLDClassifierTest

Refactoring the code so that it allows a better instrumentation. Avoids
remote calls to unavailable WFS server.
Repairing Mapfishapp's testsuite

- Using directly JSONObject instead of a StringBuilder for building JSON
to be sent to MFApp's code.
- fixing testChoropleths test.
Fixing Mapfishapp's testsuite

fixing testUniqueValues test