Make binaries presigned by default

[Atemu]

AFAIK this allows re-signing the apps provided by robotnix using your own keys. I've never used signing though and it's therefore also unmaintained.

This quirk of robotnix prevents app stores from updating the apps though as their signature is whatever snakeoil key robotnix uses by default.

I'm thinking we should just default apps to be presigned so that they can be updated independently of robotnix by default.