TEIIDDES-2120: Fixes for Vdb and VdbEditor

* VdbEditor
 * Fixes when user files are added to a vdb. Formerly, the absolute path of the
   file was supplied to the VdbEntry even if it was in the project. Consequently,
   these files would never synchronize as they were not model resources and their
   paths could not be found in the workspace.

* VdbEntry
 * Makes the findFileInWorkspace method work a little harder to try and locate a
   resource for the given filename by navigating the files container in the vdb's
   project. This improves the chances that such files can be synchronized.

* Vdb
 * Stops udf jar files appearing in both the UDF and Other Files panels in the
   VdbEditor. Only user files should appear in the userFileEntries set.

Conflicts:
	plugins/org.teiid.designer.vdb.ui/src/org/teiid/designer/vdb/ui/editor/VdbEditor.java
	plugins/org.teiid.designer.vdb/src/org/teiid/designer/vdb/VdbEntry.java