Add a vdb reuse feature

See https://issues.jboss.org/browse/TEIID-1366, which not only replaces mergeVDB functionality, but provides a declarative way for vdbs to be reused at runtime. Designer will need to provide a representation of the reuse feature that includes:

• Optionally an artifact that represents a vdb to import, but that only contains the consumable metadata - not the transformations.
• A way to manage those imported artifacts in the context of a workspace
• A way to edit the imports in the vdb.xml to specify the name/version of what's expected at runtime
• preview would be broken unless a deployed version the re-use VDB existed

An expected flow should be available from GSS customer requests and at a high-level could be described as:

Scenario A

• Team 1 develops a vdb and exports the "reuse vdb" without transformation metadata for use by Team 2
• Team 2 develops a new vdb using the reuse vdb - no access is needed to the original vdb

Scenario B

• Team 1 develops a vdb and provides it directly to Team 2
• Team 2 uses original vdb as "source" and models new vdb from it