Add submit button component and style it.

frontend/src/app/pages/publication-edition/publication-edition.component.html

@@ -42,9 +42,7 @@
             </mat-tab-group>
             
             <footer>
-                <button type="submit">
-                    Save
-                </button>
+                <app-submit-button label="Save" [requestPending]="(isSaving$ | async) == true"></app-submit-button>
                 <button type="button" class="secondary" (click)="goPreviousLocation()">
                     Cancel
                 </button>