Filter Support in Listen decorator

[solidhtp]

Fixes #49.

Changed source type in Listen decorator to Source to support filters.

[raschan]

@solidhtp It seems like the linting plugin for github actions is still having problems with PRs from forks....
We are in the process of migrating away from github actions, hopefully that would solve this problem.

In the meanwhile, if it's all the same to you, I'll check it manually

[raschan]

@solidhtp could you fix the failing tests?

[raschan]

Currently the assumption, that the source can only be string, is running a bit deep in the code. There are a few more changes and checks required for it, to definitly work with everything that we depend on.

In the weekend I'll have more time to have a deeper look.

[solidhtp]

Thanks @raschan . This was the only change I did on my local machine to get it working. I don't have deeper understanding of the code and do not know how deep the impact would be. Please have a look. Let me know if I can help in any way.