Sharing private entries

[dandavies99]

Problem
The current permissions setup is a bit simplistic - simply having private and public entries. It is quite common for users to want to share entries (e.g. experiments) with a specific set of other users, especially while the work is ongoing.

Proposed solution

• Allow users to select other users who can also have read access to private entries they have created.
• In practice, this could be done with a "read_users" field which is updated by the owner.
• Upon saving, in the existing (or possibly a new) post-save signal the read permissions should be granted to those users for that object.
• Importantly, permissions should also be taken away from users who are not in the list (as users could be removed from the list by the owner).

Potential blockers

• Would need to check carefully how the read permission is applied in different situations e.g. when the read_only users are in different groups which already have a certain permission set for the object in question.
• This would mainly be applicable to experiments but would also need to be implemented for device specifications and batches of those devices.

Aha! Link: https://imperial-college-ict.aha.io/requirements/RSE-138-3