Add needed extra dependencies on swh-core.

requirements-swh-dev.txt

 # Add here internal Software Heritage dependencies, one per line.
--e ../swh-core
+-e ../swh-core[http,db]
 -e ../swh-model
 -e ../swh-objstorage[testing]
 -e ../swh-scheduler

requirements-swh.txt

 # Add here internal Software Heritage dependencies, one per line.
-swh.core
+swh.core[http,db]
 swh.model
 swh.objstorage[testing]
 swh.scheduler