Fix #75: Containmnet principle implemented

[antoineatstariongroup]

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Description

Fix #75

This PR includes:

• ContainerList implementation to automatically set parent value of a newly adding/removed element
• Properties that are part of the composite aggregation (owner/owning properties) are accessible only via readonly accessor.
• Extension methods allow to set the container of an element, by specifying the parent, the relationship to be used and the child instance