[Enhancement] Enable Saving + Opening Projects from LocalStorage

[hydrosquall]

Nature of issue?

• Presently, if someone attempts the editor without an internet connection, they'll be unable to save their work.
• This feature would move the application in the direction of a progressive webapp so that the editor can be used by those with intermittent/unreliable internet connections.

New feature details:

• In addition to the existing "save to cloud" feature, we could grant someone the ability to save their project to LocalStorage.
• This FR is based on the finding this behavior useful in a different web-based file editor that I've used, which supports in-browser saving of projects consisting of multiple files: https://stoplight.io/studio/

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[catarak]

Merging this into #103. I really would like to prioritize this issue!