Fix malformed version number in pvp/package.js
CatalogCache datatype works, with tests

Use `PackageVersion` within the package to mean the class `ConstraintSolver.PackageVersion`.  The imported symbol from `package-version-parser` is aliased to `PVP`.

In tests, `PackageVersion` still means the package-version-parser’s exported symbol.
Use the CatalogCache
More CatalogCache methods
Use a CatalogLoader

See comment at top of catalog-loader.js
Cleanup and prepare to accept test Catalog data