Handle extension dependencies

Because each extension is likely to introduce new dependencies, there needs to be a uniform method to handle the dependencies.

Importantly, it's not feasible to create a LEX conda package because of the size of the data, unless, the code and data were handled independently.

Options include:

Conda meta-package

By creating a conda meta-package all the dependencies could be handled via conda and this repo can be installed independently.

Simply list in a conda.yml file

This is simpler than creating a meta-package, but requires people to manage their environments directly -- something that doesn't work well for ESMs as their analysis environments are usually set up by a sys. admin, and would be hard to include LEX dependencies.

Adopt a data-only storage idea for this repository

Move the analysis code into LIVVkit proper, leaving only the data files behind. This will, however, make LIVVkit a much bigger package than needed for EVV and simple verification use.