Several fixes in npm, cgit and phab listers

This diff consists in 3 commits:

• cgit: fix cgit's task module and tests forgot some url_prefix there.

• phabricator: fix the FullPhabricatorLister task

  forgot the forge_url -> api_baseurl renaming in there.

• npm: make NpmVisitModel use the main declarative base class from core.models

  This is needed by the (refactored) db init mechanism, since this later uses the main declarative base class (thus the main MetaData instance) to gather tables to be created/dropped.

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Migrated from D1939 (view on Phabricator)