Add Xcode template for macOS game

[JohnSundell]

Similar to the Xcode template for an iOS game, we should include a template for macOS as well. The template should work the same way as its iOS counterpart, in that it provides the necessary boilerplate to get a game up and running on the Mac.

[TyrfingMjolnir]

There is a HOWTO here: https://useyourloaf.com/blog/creating-custom-xcode-project-templates/

Like this? https://github.com/TyrfingMjolnir/ImagineEngine/tree/master/XcodeTemplates/Imagine%20Engine/macOS%20Game.xctemplate

That said the original iOS template does not work; here is the error I receive for line 2 of AppDelegate.swift: import ImagineEngine No such module 'ImagineEngine' as such:

I most likely have to run some sort of npm i / yarn or whatever the equivalent is in swift, swift run? swift build? And why is this not part of the standard build procedure? pod install?!?

Why not use SPM? John?!? SPM would be more in your spirit, no?