Feature: Add clear and remove_device to ElementHolder #408

Description, motivation and use case
Add a clear() and remove_device method to ElementHolder to allow to remove elements that have been added using fill_device.

Proposed solution

In one of the tutorials we currently have:

simulator._MAGNETS.pop("QF_001", None)
simulator._ALL.pop("QF_001", None)

to be able to remove a magnet that has been attached.

It would be good to have a clear() and a remove_device method to have an easier syntax to remove a specific or all elements from the ElementHolder.

Checklist

• I've assigned this issue to a project
• I've @-mentioned relevant people