Different updates

Changed API behaviour to manage Session objects
Added route in frontend to link to API

back_end/src/main/java/hackathon/FrisbYEE/rest/SessionResource.java

@@ -42,6 +42,7 @@ public class SessionResource {
     public ResponseEntity<?> create(@RequestBody SessionDTO dto) {
         try {
             Session session = maptoEntity(dto);
+            session.setCoach(coachDAO.findById(dto.getCoachId()).orElse(null));
             sessionDAO.save(session);
             return ResponseEntity.status(HttpStatus.CREATED).body(maptoDTO(session));
         } catch (Exception ex) {