Add Luigi to requirements of swh-dataset and swh-graph

requirements-swh-dev.txt

@@ -6,10 +6,10 @@
 ../swh-auth[django]
 ../swh-core[http,db,logging]
 ../swh-counters
-../swh-dataset
+../swh-dataset[luigi]
 ../swh-deposit[server]
 ../swh-fuse
-../swh-graph
+../swh-graph[luigi]
 ../swh-icinga-plugins
 ../swh-indexer
 ../swh-journal

requirements-swh.txt

@@ -2,9 +2,10 @@
 swh.auth[django]
 swh.core[db,http,logging]
 swh.counters
+swh.dataset[luigi]
 swh.deposit[server]
 swh.fuse
-swh.graph
+swh.graph[luigi]
 swh.indexer
 swh.journal
 swh.lister