Migrate: openquake config utils from runzi

[chrisbc]

in nzshm-runzi are a bunch of openquake related features used in runzi, see/runzi/execute/openquake/util

These probably make more sense in nzshm-model from where they can be pulled in by runzi.

so, for each module:

1. clone and located nshsh-model package
2. write test coverage
3. modify runzi to use new package import

done when module list:

• init.py
• GSIM logic tree #33
• oq_build_sites.py #96
• oq_build_sources.py
• oq_disagg_sources.py
• Chore: Migrate oq_hazard_config module/class from runzi #57