Migrate to data loader class for file-based resources

[eethann]

Currently all VMA, Adoption, and TAM tables are loaded statically, in the solution init files and elsewhere.

To allow for web-based updating of the files, refactor this to use a data loader intermediary that is called to fetch any data. That data loader might load files from a local filesystem URL or from a remote host.

Next step is to estimate the amount of work needed for this task.

[denised]

We agreed to a change of scope for this item: instead of a general data-mediation approach, we would add the specific ability to override the TAM and the Adoption for a scenario. This design is documented here.

With PR #410, I've implemented the TAM portion of this work. I will not be able to get to the adoption side for a little while. (It is also possible we can assign someone else to that part of the task. TBD.)

See also Issue #406, which would be part of handling the more general case.