Update ib_broker.py

[peterfabakker]

Warn for not able to subscribe to asset

[tibkiss]

Please change the commit message. Instead of showing what has changed please detail why the change was created. I'd prefer to stick to scipy's conventions: https://docs.scipy.org/doc/numpy/dev/gitwash/development_workflow.html

Thank you.

[tibkiss]

Taken a look on CI: five testcases are failing, plus flake8 problems are present. Please address those as well.

My recommendation would be that we split this up into smaller chunks, where one PR fixes one problem.

[tibkiss]

This change became outdated. Closing.