Added return_periods and stats attributes [skip hazardlib]
Added return_periods and stats attributes [skip hazardlib]


Former-commit-id: bfd61fe7109745463d2b76b94edee5fd8c06b1fa [formerly afcbee532c4c2d842e2190cd60f091850a372e90]
Former-commit-id: bb7aad301969d9cef494ae13c1cb37fd80a473ef
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine