Added initial achievement controller

src/main/java/ntnu/idatt2016/v233/SmartMat/controller/user/AchievementController.java

+package ntnu.idatt2016.v233.SmartMat.controller.user;
+
+import lombok.AllArgsConstructor;
+import ntnu.idatt2016.v233.SmartMat.entity.user.Achievement;
+import ntnu.idatt2016.v233.SmartMat.service.user.AchievementService;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+import java.util.Optional;
+
+@AllArgsConstructor
+@RestController
+@RequestMapping("/api/achievements")
+public class AchievementController {
+    private final AchievementService achievementService;
+
+    @GetMapping("/achievement")
+    public ResponseEntity<Achievement> getAchievement(String achievementName){
+        Optional<Achievement> achievement = achievementService.getAchievement(achievementName);
+        return achievement.map(ResponseEntity::ok).orElseGet(() -> ResponseEntity.notFound().build());
+    }
+}