More control on assignments

[esyriani]

Currently, when assigning papers to reviewers (screening, QA, classification), we can only select which users and the number of reviewers per paper. The tool then randomly assigns the papers to these users according to these two constraints.

We would like to have more control on assignments by adding further constraints. One of these constraints requires to define a status for each user: junior, senior, methodologist. This is independent from reviewer/validator/project manager/admin roles.

One constraint is to specify that it should assign at least one senior reviewer per paper.

Another constraint can be to have the same reviewers assigned to a paper they have reviewed in a previous stage (e.g., previous screening phase)