Porting prep: Move settings and general logic to plain C++

[attah]

Move as much logic as possible from JavaScript to C++ and SeaPrint to ppm2pwg.

• [x] Format support checking/listing
• [x] Format conversion logic
• [x] Print job settings (beyond pure input)
• [ ] Name-prettification
• [ ] WiFi Checker
• [ ] App settings (and make backends swappable)
• [x] Everything backing the properties page
• [x] Debug JSON
• [x] Fake-printers
• [x] Saving of default job settings