some issues in Version and IVersion

[Sergio Miranda Freire]

The attribute contribution is not set in the initializer.

The invariants below are not enforced:

Contribution_valid: contribution /= Void and contribution.type.is_equal(“CONTRIBUTION”)

Preceding_version_uid_validity: uid.version_tree_id.is_first xor preceding_version_uid /= Void

Lifecycle_state_valid: lifecycle_state /= Void and then terminology(Term_id_openehr).has_code_for_group_id(Group_id_version_lifecycle_state,

lifecycle_state.defining_code)

This last invariant should be implemented through the terminological service.

Maybe it would be interesting to have a representation function for this class.