Consider adding support for velopack

[GeertvanHorrik]

Squirrel seems no longer to be actively maintained. An alternative (with a decent upgrade path) is Velopack.

We need to investigate the package and it's possibilities.

The idea is not to rename this package, but add support (and an automatic upgrade path) to velopack instead.

[caesay]

It looks like this library (from the readme) was to add extra features like channels: note that Velopack already supports channels natively.

[GeertvanHorrik]

I read about the channels, but we need a way to auto-detect what tech to use for backwards compatibility. I will check if we can keep using it as-is or whether we need to migrate our current approach.

[caesay]

Looks like you could pretty easily write an IUpdateService which wraps Velopack's UpdateManager so you can swap your backend out. Note that Velopack supports migrating apps from Squirrel automatically (but back not the other way)

[GeertvanHorrik]

See #807

[GeertvanHorrik]

Fully implemented.