Propagate errors from the Plugins to the API

[maximiliani]

State of the art

Right now, the mapping service always returns a result even, if it does not make sense or contain any information. What happens if a plugin fails (e.g. if a Python error is thrown)? Nothing. That is not sufficient, because errors can (and will) happen in the mapping plugin.

Idea

Propagate the error through all layers of the Mapping Service. Create an opportunity for plugins to throw exceptions that are returned to the consumer via the API. Extra: Implement a boilerplate that deals with Python Exceptions and automatically converts them.