Add ability to query active effects

[fattredd]

I found this helpful when trying to figure out what layer is causing certain effects.

Serves me right for trying to add layers to indicate that maintenance is due

[julianschill]

Thank you for this contribution. I was planning to add the get_state function, which is the Klipper mechanism to get information about a module. I think this can then be used with a macro and jinja to get the same functionality. I am hesitating adding an additional gcode command for that. I will keep this PR open until I have implemented it and we can decide if we still need this.

[fattredd]

Fair enough. I'm happy to hear that this will be a feature in the future regardless of how it's implemented :)