8 hour flight cannot be saved

[nguyenquyhy]

Flight over the Atlantic From JFK to Sweden hangs when i try to save for example. 8 hours. Shorter flights for exemple Stockholm-Copenhagen works fine.

Investigation: Serialize/Deserialize a large list into string take a really long time and can lead to OOM. A better way would be to do that directly on stream.

• Async for saving and loading
• Add Saving & Loading states and disable controls appropriately
• Handle reverting back to correct state on error
• Handle exiting

[nguyenquyhy]

Released in v0.14