For code review

Added status messages for queries in progress.

Replaced all maps in the handleMessage method with the MessageStruct,
except for the final result, as this one uses the key 'values', where
the rest use the key 'value'. Once this has been changed in the frontend
it will be updated in the backend as well.

Wow! (with Joris + Lorenzo)

In case you want to edit stuff

Most of this code was taken straight from the schema service. No tests
were written because this is entirely dependent on external
dependencies.