Impelement Accordion bevavior for meta fieldsets on node form

Problem/Motivation:

Currently the "meta" fieldsets on the node form are kept open when you open another one. In the extreme, you could come to a situation like this:

They should be open only one at a time. The current beavior is basically Drupal 6 and something that was meant to be moved away from: fieldsets that open and stack upon the other.
Since the seperating titles are not very strong as seperators, the situation becomes hard to handle if you open more than one fieldset. One has a hard time to seperate the fieldsets visually, which is worse because they have a grey background and tend to become one block.
It is an issue similar to #2009930: Do not keep meta fields of node form open when they have a value, even though this applies more to the meta fieldsets itself and not the balance with the contend edit part.

Personally, I find it hard to fucus on the thing I just wanted to edit.
I think there was a plan to implement accordion behavior here which should not be too hard technically. Because the open fieldsets have a darker background than the closed ones, this fact could then be used to keep focus of the currently open fieldset.

Proposes Solution:

Implement Accordion behavior.