Support Paper-Reviewer assignment with no anonimity

[melisabok]

Currently the set_assignment function is calling to the tools module to create an AnonReviewer group even if the reviewer name is public. We should skip this.

We need to also modify the webfields to read the data without expecting AnonReviewers group.

[melisabok]

We should add a test for a venue with no anonymity and I think the assignment would work because with the new anonids feature, the assignment process is adding a member to a paper group. We should add a parameter to create_paper_groups where anonids=True only when the reviewers are no anonymous.