Implement "Update item from WikiData"

[timconrad]

As a first step to #83 , we should have a functionality that checks the current item, compares to the information on, say Wikidata, and add missing our updated information.

The (flask based) Rest-API (based on the MaRDI importer) should have most of this functionality already implemented.

Things to do:

• Implement the update logic (needs to be done carefully!)
• Change the current SpecialPage to include this
• Later: Add a "Button" at the profile page