Replace numpy arrays with postgres array fields in output tables

As the output tables will become part of the "interface" between oq-engine and other software (like oq-platform) we want to use more portable data type. Thus, this pull request replaces all the blob fields holding numpy arrays with Postgres float[] arrays.

Related ticket: https://blueprints.launchpad.net/oq-platform/+spec/icebox-geonoe

For a clean diff https://github.com/gem/oq-engine/pull/1300 should land first.