Add support for the new index database

[ewoutkramer]

Grahame has added a CAR-file like sqlite file to the NPM packages which is probably replacing the index.json file and might help to deal with bigger NPM files, since the files are indexed in sqlite instead of json.

We should probably take a look at this file and see whether it suffices for us, and otherwise maybe suggest changes to Grahame so we can use the same file (and no longer need our own index even???).