Escape ltree input

[jjeising]

The ltree extension only supports A-Za-z0-9_. Other characters, even in conditions cause Syntax errors which cause exceptions. We need to filter input at least for search, probably also for property creation.

Or maybe just drop ltree and use strings? I'm currently not sure if we use any features.

[pegro]

We are not using ltree features as far as I can tell. In the API handler I only use the model and I didn't find any operators specific to ltree there. So I guess using strings is fine. Maybe defining an own regex in a check contraint would be a good idea, e.g. for prohibiting spaces or equal signs, which might break things somewhere else.