Imported mean_curve and quantile_curve from hazardlib
Imported mean_curve and quantile_curve from hazardlib


Former-commit-id: 30380ff11260a2e6fa56e14a53a095f09ddd6878 [formerly f58b5f6c2920c846f053c49797dd5e961232843e]
Former-commit-id: 90473dd2a670813ee0641d992df1e223b9b02920
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine