Add copyright header to all LimeSurvey application files that are missing it
completed by: Lekov
mentors: Carsten Schmitz (c_schmitz), Pieter-Jan Speelmans (MrP001), Tom Klingenberg (mot2), Shubham Sachdeva, TMSWhite, Diogo Gonçalves (dionet)
Do as the task title says. Before you start please contact one of the mentors to discuss the exact implementation.