Refactor views/ObjectDataView.vue to improve clearness

[astanik]

Change embedded DataTables to TreeTable.

TreeTable Columns: Titel | Type | Beschreibung | Mieter | Fläche | Buttons zum Hinzufügen, Ändern und Löschen

An empty column at the bottom of each segment should have just a Button zum Hinzufügen of an object of that type.

Info:

• https://sakai.primevue.org/uikit/tree
• https://primevue.org/treetable/#template

Requirements:

• The backend must return with GET /api/v1/projects/{projectId}/properties a nested list of all objects (properties, buildings, etc.).

[ChristopherDKeller]

I'd like to complete this issue. Edit: I just saw that someone was quicker.

[astanik]

@mesyamaureen Unfortunately, I have already discussed with @ChristopherDKeller about this issue and promised him that he would implement it. This issue also requires adjustments at the backend.