TEIIDDES-1739 DDL Importer modifications

Additional Modifications for the DDL Importer and Teiid Connection Importer:
- Modified DdlImporter to create a RelationalModel instead of Emf artifacts
- Improvements to RelationalModel, RelationalReference and associated classes
- Added EMF to RelationalModel converter
- Added difference generator for comparison of two RelationalModels
- Added generator which creates or updates an EMF model, given a difference report
- Replaced EMF comparison page in the import wizards
- Adapted Teiid Connection importer