115046: Fixed multiple edit relationship bugs

- Fixed issue making it impossible to add new relationships until the page is refreshed after deleting an existing one (only when you refreshed the page after creating the initial relationship)
- Fixed NPE in DsDynamicLookupRelationModalComponent
- Grouped buttons on relationship page in order to assure that they always have the same behaviour

src/app/item-page/edit-item-page/abstract-item-update/abstract-item-update.component.ts

@@ -55,6 +55,10 @@ export class AbstractItemUpdateComponent extends AbstractTrackableComponent impl
    */
   updates$: Observable<FieldUpdates>;
 
+  hasChanges$: Observable<boolean>;
+
+  isReinstatable$: Observable<boolean>;
+
   /**
    * Route to the item's page
    */
@@ -101,10 +105,9 @@ export class AbstractItemUpdateComponent extends AbstractTrackableComponent impl
     }
 
     this.discardTimeOut = environment.item.edit.undoTimeout;
-    this.url = this.router.url;
-    if (this.url.indexOf('?') > 0) {
-      this.url = this.url.substr(0, this.url.indexOf('?'));
-    }
+    this.url = this.router.url.split('?')[0];
+    this.hasChanges$ = this.hasChanges();
+    this.isReinstatable$ = this.isReinstatable();
     this.hasChanges().pipe(first()).subscribe((hasChanges) => {
       if (!hasChanges) {
         this.initializeOriginalFields();