write all cdts tables even if stories do not exist; fix bug in write_gexf that didn't write media codes
write all cdts tables even if stories do not exist; fix bug in write_gexf that didn't write media codes

AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,berkmancenter/mediacloud,berkmancenter/mediacloud,berkmancenter/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,berkmancenter/mediacloud,berkmancenter/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud,AchyuthIIIT/mediacloud