Deep copier in its own package

[Ducasse]

Let us see if this is working.

fixDependents
	"They are not used much, but need to be right"

	^ DependentsManager fixDependents: references

introduces a dependency from deepCopier to System-Model but we will see.

[Ducasse]

The design of the deepcopier is strange since most of the logic is in Object and not in the deepCopier.

[Ducasse]

Broken tests do not seem related.