API Versioning for datastore (+ tracingstore?)

[fm3]

We should introduce API versioning for the routes of the datastore (and possibly the tracingstore) in the same fashion as we already have it for the wk api routes (webknossos.versioned.routes).

This way we don’t have to keep the current API backwards compatible forever (or at least the parts that are used by the libs datastore client and voxelytics).