Dependencies mismatch and clarification on InMemoryStore

Dear Maintainers,

I was wondering if this is a completed reference version using the `hub-node-core` or a work in progress. I am trying to build the project and have been facing a bunch of issues with the build and getting the server to work.

The `package.json` file refers to the `hub-node-core` which isn't available on `npm` directly as `npm i hub-node-core` and is instead `@decentralized-identity/hub-node-core`. Changing it to this helps me fetch the required dependencies at `0.1.0` while the core is at `0.1.4` version.

Additionally, I am unable to find the `InMemoryStore` class referenced in [`router.ts`](https://github.com/decentralized-identity/hub-reference/blob/master/src/router.ts#L3) which tries to import it from `hub-node-core` but it looks like it doesn't exist. Is the `InMemoryStore` module expected in the `hub-node-core` or is this an in-memory `Map<>` implementation in the `hub-reference` project?

I'd be happy to help and contribute.