More specific emailing for course specific roles

We should discuss what changes are necessary regarding emailing users with roles.

Distinct should be applied on the set of users to avoid double emails.

NOTE: check whether emails are sent to unregistered users (course-specific roles linked to a name and an email but not a user).

We can have a cocoon-style selection menu where you can add recipients to messages. Possible options for this menu:

• clients of approved projects (requested by SP, TM)
• clients of pending projects
• clients of all projects (approved, pending, and rejected)
• users with a particular role assigned to approved projects (requested by TM)
• users with a particular role assigned to all projects (approved, pending, and rejected)
• users with a particular role assigned to groups approved by the client
• users with a particular role assigned to fully approved groups (by the client and the coordinator) (requested by SP, TM)
• users with a particular role assigned to all groups (no matter what their status is) (requested by TM)
• students who are approved for the course, but not in an approved group (requested by SP)
• clients of fully approved groups (by the client and the coordinator) from the year before (to ask them to submit a new proposal) (requested by SP but already covered by simply sending an email on behalf of the previous course edition?)
• clients of projects without groups (requested by TM)
  • should be verified if they actually mean "without fully approved groups" instead