feat: add individual collection sheet (#1204)

Fixes: #255

src/app/collections/collections.service.spec.ts

@@ -0,0 +1,12 @@
+import { TestBed } from '@angular/core/testing';
+
+import { CollectionsService } from './collections.service';
+
+describe('CollectionsService', () => {
+  beforeEach(() => TestBed.configureTestingModule({}));
+
+  it('should be created', () => {
+    const service: CollectionsService = TestBed.get(CollectionsService);
+    expect(service).toBeTruthy();
+  });
+});