Make UHS/Disaggregation results more web-friendly

[Lars Butler]

In a discussion with Philipp Kästli, it was pointed that the hybrid results (binary files soft-linked in NRML XML) produced by UHS and Disaggregation calculation are problematic if NRML is to be used as an exchange (import/export) format.

Example:
- A UHS or Disagg calculation is run
- Results are serialized to the db
- User requests an export of the data
- HDF5 data needs to be created from the database data (note: at the time this bug was filed, no UHS or Disagg results are yet stored in the database; they will be in the future)
- The NRML wrapper can be serialized, but needs to provide nice links to the HDF5 files
- Currently, the 'path' to each binary HDF5 file is assumed to be a NFS path.
  - To make this more export-friendly, these paths could instead be a URL (which could be either a direct link to the file, or the URL of a REST API endpoint which serves up the file to an authenticated user)

[Launchpad Janitor (janitor)]

[Expired for OpenQuake because there has been no activity for 60 days.]