Server Side
Added has_many through on Intervention and User model.
Each intervention can have many collaborators trhough
join model Collaboration.

The reverse is also true. A collaborator (User) can
have many partecipations (in interventions).
Client Side
Added collaborators management in EditInterventionCtrl
Server side
Modified RPS
Server Side
Added Name column to User
Modified RPS module to show collaborators' name in groups of 3 per row
Server Side
Modified RPS module to group collaborators in 4 and include intervention's user.