[Management] manage XSD via JMX

[dsukhoroslov]

• add/delete XSDs via JMX (add already done!);
• separate XSD handling in another Management interface?
• use custom types from XSD;
• store XSD as is on FS and load it before schema documents;
• restore an ability to load many schemas (with imports) in one hit;
• use registered XSDs for binding;
• what about similar approach for JSON?

[dsukhoroslov]

• can also use and turn on/off incoming document validation via XSD

[dsukhoroslov]

done schema handling via ContentModeler interface. XML/JSON schemas are processed currently.