Tidies up CTDBP work

- Replaces seawater.gibbs with pygsw.vectors (better numpy support)
- Adds pygsw as dependency to coi-services
- Adds extensive test cleanups
- lat/lon should not be in CFG it should be under process so that we
  don't clobber global configurations by accident (especially in tests!)
Gets rid of seawater.gibbs and more cleanup
Merge pull request #692 from lukecampbell/ctdp_contribs

Tidy up CTDBP transforms