Fix add existing tree to annotation

[MatthisCl]

Description:

• When trying to deepcopy a group, hashfunction is needed before initialization. This leads to an error as self._id is not set before initialization. One could change the hashfunction to not be dependent on the id or change the hashfunction

Issues:

• fixes Cannot add existing tree to new annotation #1197

Todos:

Make sure to delete unnecessary points or to check all before merging:

• Updated Changelog
• Added / Updated Tests

[philippotto]

this class inherits from group which also defines __eq__, right? couldn't the method here be omitted?

[markbader]

Yes, I think I tested it before, but it didn't work. I just figured that @attr.define adds a standard __eq__ implementation. This can be avoided when adding @attr.define(eq=False). Thanks for mentioning it, I removed the __eq__ and the __hash__ method from the Skeleton class.

[philippotto]

great, thank you!