Resolve "Extract valuable changes of closed merge request !428"

Summary

After careful consideration merge request !428 (closed) has been dropped and closed. While working on resolving the underlying issue, other changes have been made, what this merge request ist attempting to retain. These include:

1. Fixed problems with instantiation of node attribute horizon
2. Fix from_dict not considering all ForecastSolarNode attributes
3. Simplification by removing attributes time, limit, start and transit, as their API use can effectively be handled by the user.
4. Cover remaining attributes intensively in testing and include more sample data for mock responses

Minor:

• Update test_example correspondingly
• Fixed response data's column naming
• Minor fix of field_transform in node instantiation
• Typos and the like

Closes #319 (closed)