Implement entity container

Properties of the EntityContainer class:

1. the container takes care of when information is written to the underlying entity
2. the container implements the mantle_api::IEntity interface
3. set operations are stored in the container state while get operations pull from the underlying entity
4. the UpdateEntity function writes the state of the container in the underlying entity
5. the initial state of the container is the same as the underlying entity

CI job: https://ci.eclipse.org/openpass/job/GtGenCore/view/change-requests/job/MR-146/