[Architecture] Spike - Identify work needed for migrating `state`

In the [PoC branch](https://github.com/Automattic/woocommerce-services/compare/tweak/poc-architecture-meetup-v2) we still have `wp-calypso` as a folder (but not a submodule). It isn't really calypso, just a very small subset of it. Refer to `WooCommerce Services Architecture` p2 for more info.

The goal of this spike is to figure out what needs to be done in order to migrate `state` out of that folder and into the extension root folder. It'll probably require some roundtable discussion.

Open the PoC branch comparison and the “WooCommerce Services Architecture” document, page 2; inspect the wp-calypso folder and its state subset. Identify the work needed to move state into the extension root and use the proposed roundtable discussion to resolve scope. Done means an agreed migration checklist.

Written by the indexing model from the issue text.