Proposal: new "Tech Support" user role

[rmunn]

As a follow-up to #1458, we might want to consider a "Tech Support" role in Lexbox. It would be similar to regular users (e.g., would not be given admin privileges) but would be allowed to temporarily join projects without needing manager approval.

In Language Depot back in the Redmine era, there were lots of projects that had three or four members with the Tech Support role that lingered for years; to avoid that situation in Lexbox, I propose that when a user with the tech-support role joins a project, they have a checkbox (checked by default) that says "auto-remove me from the project after one week". Then a Quartz job is queued up to do the removal. If they uncheck the box, then they can go through the normal joining process subject to manager approval, and they can join as a regular (permanent) user.

Thoughts?