Core: Add backref in traits to their object

[IoannisP-ITENG]

Core: Add backref in traits to their object

Description

Add backref to faebrykliboject when making trait part of object.
Remove manual backlinks in traits that used those before.

Fixes #49

PR type

• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• My code follows the coding guidelines of this project
• My PR title is following the contribution guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

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