Rename Collaboration to LegacyCollaboration (rename table too)

[#79005958]

This is part of the bigger migration / change of the collaboration
object structure.
Add new collaboration model and table, fix c. membership filename typo

[#79005958]
Update collaboration memberships table (add namespace, rm access_token)

[#79005958]

Token will be obtained directly from the user model.
Add one-to-one relationship between collaboration and bundle content

[#79005958]
Generate new collaboration data using legacy collaborations (migration)

[#79005958]
Use new collaboration model instead of legacy one

[#79005958]
Update specs related to collaborators

[#79005958]
Fix a bug that was causing endless copy cycle of students data

[#79005958]