Save & load config

[TimPietrusky]

Instead of only having the config in the localStorage, it would be nice to save it somewhere else to, so it can be easily exchanged with other users.

• Save config locally: https://scotch.io/tutorials/use-the-html5-file-api-to-work-with-files-locally-in-the-browser
• Save config into a storage provider (e.g. Google Drive)