[editor] Fix section counter update

New section components no longer get their number on creation. This has 
the effect that the section gets a new number and is updated again with 
all others after that.
Numbering of all sections is triggered in one place (UnitService) and 
updates all existing sections.

projects/editor/src/app/components/unit-view/section/section.component.ts

@@ -72,7 +72,7 @@ import { SectionCounter } from 'common/util/section-counter';
     .section-wrapper .section {flex-grow: 1;}
   `
 })
-export class SectionComponent implements OnInit {
+export class SectionComponent {
   @Input() section!: Section;
   @Input() sectionIndex!: number;
   @Input() lastSectionIndex!: number;
@@ -88,10 +88,6 @@ export class SectionComponent implements OnInit {
               public elementService: ElementService,
               public sectionService: SectionService) { }
 
-  ngOnInit(): void {
-    this.updateSectionCounter();
-  }
-
   updateSectionCounter(): void {
     this.sectionCounter = undefined;
     if (this.unitService.unit.enableSectionNumbering &&

projects/editor/src/app/services/unit-services/section.service.ts

@@ -41,6 +41,7 @@ export class SectionService {
         page.addSection(section, sectionIndex);
         this.selectionService.selectedSectionIndex =
           Math.max(0, this.selectionService.selectedSectionIndex - 1);
+        this.unitService.updateSectionCounter();
         return { section, sectionIndex };
       },
       rollback: (deletedData: Record<string, unknown>) => {
@@ -53,6 +54,7 @@ export class SectionService {
         page.deleteSection(sectionIndex);
         this.selectionService.selectedSectionIndex =
           Math.max(0, this.selectionService.selectedSectionIndex - 1);
+        this.unitService.updateSectionCounter();
       }
     });
   }
@@ -130,12 +132,14 @@ export class SectionService {
     page.deleteSection(sectionIndex);
     page.addSection(newSection, sectionIndex);
     this.unitService.updateUnitDefinition();
+    this.unitService.updateSectionCounter();
   }
 
   insertSection(pageIndex: number, sectionIndex: number, newSection: Section): void {
     const page = this.unitService.unit.pages[pageIndex];
     page.addSection(newSection, sectionIndex);
     this.unitService.updateUnitDefinition();
+    this.unitService.updateSectionCounter();
   }
 
   /* Move element between sections */