Make close button of exercise details less prominent

This makes it look like the other buttons in the modal, i.e. with an outline and white background.

This is a design choice. I prefer the close button to look like the other buttons, not like a focused button. If we want to keep the previous style just comment and close this merge request.

src/main/webapp/app/exercise/exercise-details/exercise-details.component.html

@@ -83,7 +83,7 @@
                                 </button> -->
                                 <div [ngbTooltip]="helpCommingSoon" placement="bottom">
                                 <button *ngIf="exercise.type == exerciseType.COLLECTION" type="button" class="btn btn-outline-secondary"
-                                    style="display: block; margin-bottom: 5px;" 
+                                    style="display: block; margin-bottom: 5px;"
                                     jhiTranslate="exercise.details.allExercises"
                                     disabled>
                                     >
@@ -341,7 +341,7 @@
 
                 <!-- Modal footer -->
                 <div class="modal-footer">
-                    <button type="button" class="btn btn-secondary" data-dismiss="modal"
+                    <button type="button" class="btn btn-outline-secondary" data-dismiss="modal"
                         jhiTranslate="exercise.close"></button>
                 </div>