Ensure get_dynamic_item does not modify object

[philippjfr]

So this was a pretty nasty bug, turns out my usage of .map with clone=False was modifying the object causing various weird bugs. This PR is a bit of an ugly workaround updating the item in DynamicMaps using a map call that doesn't modify the object and updates it and a separate map call to actually get the item. Can't think of a better to solution to update composite objects (i.e. Layouts and AdjointLayout) containing dimensionless DynamicMaps since select won't work.

[jlstevens]

Would calling select without arguments having the same effect as [()] for dimensionless dynamicmaps help (or at least appear more consistent)?

Otherwise, I'm happy to merge although I have to admit I have difficulty following this code (because it is a complicated thing to do..not because I think it is badly written).

[philippjfr]

Would calling select without arguments having the same effect as [()] for dimensionless dynamicmaps help (or at least appear more consistent)?

I would like it if there was some way of doing this via select but I currently don't see select without arguments working in that case because select ends up being called for all kinds of things, often without specifying any valid dimensions for that particular object. Let's merge for now, and I'll keep thinking about it, this PR fixes some fairly nasty bugs so I'd like it merged now. Let's revisit when we look at counter mode, which faces similar hairy issues as dimensionless DynamicMaps.

[jlstevens]

Sure. Merging!