Add function to populate/update CVs in an existing database

[horsburgh]

There is a script in the ODM2 repository now that does the initial population of the CVs for a blank ODM2 database. We should add a function to the ODM2 API that updates the CVs:

UpdateCVs(IncludeUnits = "True")

There should be an option for including the Units (or not) since it is not a CV. We might also want to add a flag that specifies what to do with terms that might be in the database, but don't match terms in the master CV.

[emiliom]

https://github.com/ODM2/ODM2/tree/master/src/load_cvs

[emiliom]

I'd thought about that script, too, and how to pull it out the ODM2 repo and make it more visible/accessible.

A couple of comments:

• Currently it doesn't use odm2api. So while it has similarities in function to some of what odm2api does, it's actually completely independent.
• Browsing the code, I think all the "CV Objects" definitions are doing the same thing already being done in odm2api. If that's true, in principle, all that could be replaced by relying on odm2api instead. Pro: make load_cvs.py MUCH easier to maintain and more lightweight; Con: adds another dependency.

Either in its current state or if it were overhauled to use odm2api, I wonder if the odm2api repo is where it best fits (but as a stand-alone "utility"), or if there's a better repo (maybe a new one) for it, to keep odm2api leaner.