Create explicit hash storage and retrieval methods in the new entity storage classes

[ghost]

User story:

As an admin, when using the new custom entity system I would like to see readable titles for all my metadata so that I can find what I'm looking for.

Acceptance criteria:

• We can submit new data and the entities for the datasets are created.
• We can see readable titles for all created entities.
• Hashes are stored separately from the titles but referencer still works.

Blocked by #3321 Merge again the feature branch.

Estimate:

2 days