[Developer] Backup user files during editing

**Is your feature request related to a problem? Please describe.**
Ref https://community.software.sil.org/t/i-just-overwrote-my-keyboard/3045

>Does Keyman Developer keep backups of your files? The program wasn’t compiling, and suggested it was because my file name had capital letters. (I’m not sure if that was actually the problem.) While trying to rename the program, I ended up overwriting it with an empty template. Is there any way to salvage it?

**Describe the solution you'd like**
Two parts:
1. Backup of work automatically as you save. Perhaps using git?
2. Autosave / auto-backup for long lived edit sessions.