`isinstance()` instead of `eval`

[hrshdhgd]

This fixes a few other things that came to light:

• [x] We need to pass the value of the Token object and not the entire object. This is done by

  new_token = extract(tree, "new_label")
  new_value, representation = get_entity_representation(new_token)

  I was directly passing new_token to the (say) NodeRename class which messed things up and there were weird strings with the class name Token in them.

• [x] This PR automatically fixes the extra quotes in the tokens since get_entity_representation() which was not called earlier takes care of it.

This PR overrides #69 rendering it redundant and a hacky solution