The `GenesisJsonProvider` implements the `ethers.Provider`
interface and is constructed with a geth genesis file, either
as an object or as a file to be read from disk. It implements
a subset of the RPC methods that use the genesis file
as the backing storage. It includes tests for its correctness.
Not all methods are implemented, just the ones for the regenesis
testing.

This PR also moves the tests around in the `core-utils` package
as some of the tests were being skipped. The `tests` directory is
flattened, having so many subdirectories was not needed. The
`package.json` test script is updated to ensure that all tests
are run.

Also add some deps that are required for the `GenesisJsonProvider`.