Add support exporting the Designer VDB as Dynamic VDB

When a VDB is developed in the Designer, provide an option to export the given VDB as Dynamic VDB, which is simple XML format using DDL.

The server already provides mechanism to retrieve the schema (DDL) for a given model. Using this technique of retrieving the DDL, this feature can be built.

One caveat is support for XML document models in Dynamic VDB. When VDB contains XML document model, do not support this feature.

This has couple benefits

• Users can use these in Teiid for simplified usage.
• Can used to check the models into source repository like GIT or SVN etc and compare with later versions for modifications
• Open Shift

As for importing of Dynamic VDB, that can be handled as separate issue.