v2.3.1

A quick fix for 2.3.0: the app could stall right after updating while it made photo thumbnails, and now it doesn't.

⚡ Improvements

• Feedback on every click: a thin progress bar runs across the top while a page loads for the first time. Once the first screen is up, the other pages load in the background, so later clicks open right away.
• Lighter compression: responses use a lighter gzip setting. Files are nearly as small and the server, such as a Raspberry Pi, uses far less CPU.

🐛 Bug Fixes

• No more stall after updating: 2.3.0 made thumbnails when a page first asked for them, so the first vehicle list could start over a hundred at once and hold up every other request. Thumbnails are now made when a photo is saved. Photos from before, or restored from a backup, get theirs one at a time in the background, and show the full photo until then.
• Offline photo cache: the app no longer caches a full photo that stands in for a thumbnail not made yet.

📝 Tests

• Thumbnail tests updated: one is made when a photo is saved, and a missing one is filled in by the background job.