Periodic save to temp file for crash recovery

**Is your feature request related to a problem? Please describe.**
If SF2 (or my computer) crashes I have lost my work

**Describe the solution you'd like**
When starting SF2 after a crash, I get a pop up that allows me to restore the last automatically saved .sf2 file.

**Describe alternatives you've considered**
Pressing CTRL-S everytime I change something significant
