Persist unit cell

[smburdick]

Is your feature request related to a problem? Please describe. When the page closes or reloads, user loses the unit cell they've created, in addition to any plaquettes they've made

Describe the solution you'd like When the user creates a unit cell, it should be saved to their local storage, and when starting the app, be presented the option to load an existing unit cell.

• [x] When user specifies a unit cell, save it to the Redux store.
• [ ] When the app starts, check the Redux store. If there's a unit cell, offer to populate the grid, otherwise proceed as-is

Once this is implemented, we can move on to plaquettes, templates, circuits, etc.

These can also be saved to the backend, if/when user login info is stored and tied to constructed circuits.

Describe alternatives you've considered Task 2 integration will proceed asynchronously to this. Once more circuit components are added, we can persist those as well.

[smburdick]

There can be a dedicated "Save" button, but saving it to the browser cache or the cloud (once logins are established) are fine. This will be especially important for templating.

[smburdick]

Need to define this user story a little better