JAMS Sanity checks and logging

[jonnybluesman]

As part of a family of tools to validate ChoCo before exporting, we should validate each namespace and generate 2 outputs: (i) a logging file with all the violations for each JAMS (per namespace); and (ii) a coverage metric to tell us the amount of fully legal JAMS / namespaces.

We already have extensive validation support in jams_test.