Fix appx builds

[adlk]

This PR splits the Appveyor CI builds into two separate steps as the binaries that are being used to generate the appx package needs to be unsigned.

• Default generates the signed binaries and the signed NSIS .exe installer
• AppX generates an unsigned binary and appx package

If the binary is signed prior to creating the appx – the publisher info for the appx is being pulled from the certificate instead of the provided publisher config from electron-builder-appx.json

[roundhill]

Tested a build on Windows Store and it worked great (but is x86, which may actually be better for us). As discussed can you add another signed .appx build that we can test locally?

[adlk]

@roundhill you now have 3 build jobs for

• signed production build (.exe)
• unsigned Windows Store build (.appx)
• signed Windows Store test build (.appx)

[roundhill]

Thanks @adlk! once conflicts are resolved!