feat(caldav): import caldav categories as Labels (#1413)

Resolves #1274

Co-authored-by: ce72 <christoph.ernst72@googlemail.com>
Reviewed-on: https://kolaente.dev/vikunja/api/pulls/1413
Reviewed-by: konrad <k@knt.li>
Co-authored-by: cernst <ce72@noreply.kolaente.de>
Co-committed-by: cernst <ce72@noreply.kolaente.de>

pkg/models/kanban_test.go

@@ -147,7 +147,7 @@ func TestBucket_Delete(t *testing.T) {
 		tasks := []*Task{}
 		err = s.Where("bucket_id = ?", 1).Find(&tasks)
 		assert.NoError(t, err)
-		assert.Len(t, tasks, 15)
+		assert.Len(t, tasks, 16)
 		db.AssertMissing(t, "buckets", map[string]interface{}{
 			"id":      2,
 			"list_id": 1,