Simplified enum constant naming

Use the same language as the GUI to make it easier when talking about the states.

core/src/main/java/se/su/dsv/scipro/project/ReflectionStatus.java

@@ -3,5 +3,5 @@ package se.su.dsv.scipro.project;
 public enum ReflectionStatus {
     NOT_SUBMITTED,
     SUBMITTED,
-    COMPLETION_REQUESTED
+    IMPROVEMENTS_NEEDED
 }

core/src/main/java/se/su/dsv/scipro/reflection/ReflectionServiceImpl.java

@@ -60,7 +60,7 @@ class ReflectionServiceImpl implements ReflectionService {
     public void requestNewReflection(Project project, User user) {
         authorRepository.findByProjectAndUser(project, user)
                 .ifPresent(author -> {
-                    author.setReflectionStatus(ReflectionStatus.COMPLETION_REQUESTED);
+                    author.setReflectionStatus(ReflectionStatus.IMPROVEMENTS_NEEDED);
                 });
     }
 }