Issue #279: don't save empty badge

src/features/ePocFlow/ePocFlow.vue

src/features/ePocFlow/nodes/ActivityNode.vue

src/features/ePocFlow/nodes/ChapterNode.vue

src/features/ePocFlow/nodes/PageNode.vue

src/features/ePocFlow/nodes/content/DraggableNode.vue

src/features/ePocFlow/nodes/ePocNode.vue

src/features/forms/FormPanel.vue

src/shared/services/editor.service.ts

src/shared/services/graph.service.ts

src/shared/services/graph/badge.service.ts

src/shared/services/graph/content.service.ts

src/shared/services/graph/element.service.ts

src/shared/services/graph/index.ts

src/shared/services/graph/node.service.ts

src/shared/services/import.service.ts

src/shared/services/index.ts

src/shared/services/undoRedo.service.ts

src/shared/stores/editorStore.ts