job/__init__: save number of logic tree samples in uiapi.job_stats table
job/__init__: save number of logic tree samples in uiapi.job_stats table


Former-commit-id: 462ddb7cd6292cf074f2f3c35fd9587f8a00823c [formerly 462ddb7cd6292cf074f2f3c35fd9587f8a00823c [formerly 2d570d6444ddbe0e664b669fa823bf93bc2b2613]]
Former-commit-id: 47e06a701342ac742e4aa8ebb11497755c542588
Former-commit-id: 7685927ab64fc9e41993228b7e64a12f1bbc3642
gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine,gem/oq-engine