Create user-facing scaffolding functions

[cwerner]

Currently there is no procedure in place to build a valid STA setup (it's up to the user to post entities in the correct order/ with correct links between the entities). Thus we should provide dedicated scaffolding functions to easily create a valid STA setup conforming our schema.
At the moment something like this is already done in the test section in conftest.py (see setup_system function) to ramp up a simple test database with a minimal set of things, datastreams and some data.

If we refactor them into the tools section of the library they might become more universally useful if they can be fed with a schema definition (yaml, json?).