[dataimport] Uniformize the API across the different stores. This is achieved by modifying the ``relate`` method so that it takes an extra ``**kwargs``. More specifically, ``SQLGenObjectStore``'s ``relate`` method needs the the type of the subject entity which is passed through ``**kwargs`` as the ``subjtype`` keyword argument. Actually, it is the ``add_relation`` method of the ``SQLGenObjectStore`` who needs this argument. However, as this method is not called directly (but via the ``relate`` method), the ``subjtype`` argument is passed to ``add_relation`` via ``relate``. The other stores' ``relate`` methods do not need this extra argument, hence for the other stores ``**kwargs`` is empty. In this manner, the API is unified across the different stores.

[data] Add a CSS for undo UI rendering The nesting of ordered list and unordered list was badly handled. This has gone unoticed becaused it was not used. But the undo feature use this markup to render the changesets. That's why this minor change to ths CSS is introduced.