Possibility to create/edit user defined trees

[joergreichert]

Current state: we only can display trees that are provided by the official Baumkataster. So only the street trees owned by the city excluding park trees, cemetery trees, trees belonging to housing associations (even when the belong to the city) and of course no private trees.

Motivation: It can be confusing for users who just see the tree in reality but not in the app (they don't care to whom it belongs). So it should be possible to create trees manually in the app (maybe only visible to the user who had created it, but maybe later also for other users, when the existance has been verified by multiple users).

Future state: Like Giesst Koelle there is a possibilty to create new trees in the app (with position, type and age, ect.)