feat(metadata): Enable metadata editing in article edit screen

+ refactor UI of article edit screen
+ add most of the metadata in let tabpane
+ make service for mocking vocabularies
I agree, but just hiding an api error is not really ok as well. I know this is not happening only here but we should have a way to show this kind of errors, maybe even switch the app to offline mode if the backend is no longer reachable.
Just wanted to trigger the discussion on this.