Attribute changes to a graph to the user account and Item

[RaphaelWimmer]

As a user, I want that all changes I make to the graph in any frontend are attributed to me when saving the changes:

• all modifications are done via my MediaWiki user account (essential), see Issue User Auth #7
• when an item is created or modified, statements "created by" or "modified by" and "on" are added to the modified Item (optional)
• when a statement is created or modified, qualifiers "created by" or "modified by" and "on" is added to the modified Item (optional)

(Note: Data can also be added retroactively or on submission through a bot)