Enable processing fromer featured articles, code improvements

Core version is wikidata based.
Now we retrieve former featured articles categories from wikidata
and process it like the others.

Code improvements:
- use Site.fromDBName() -- thanks pyfisch
- setup task while initializing

Change-Id: Ia79913644322a9037a090912b4a8b4369705bd00
Merge "Enable processing fromer featured articles, code improvements"