Importing a VFC results in any interface implementation details in the VFC being lost

Proposed solution:
During import of VFC, any interface implementation details will be parsed and stored in the InterfaceDefinition
During csar creation, the assumption currently is that the implementation name will refer to an artifact in SDC which is connected to the service. However, when the implementation artifact name is set in the imported VFC then it should be treated as a literal value rather than a reference to an artifact in SDC
Proposal is to set the value in quotes during VFC import to indicate the value is to be used as a literal rather than a reference. Csar generation code will be updated 1) to use the value as is when it is a literal value and 2) to not to attempt to include the implementation artifact in the csar