Add CPack NSIS Windows Installer

[Trihedraf]

This adds a CPack Generator for a Windows Installer. To add to cmake command is -DWIN_NSIS=ON.

Install

Uninstall

[AJenbo]

Good old NSIS, I used to dable in it back in the day and make custom installers for various games and applications which had awfuller installation processes.

I have noticed that a large lumber of .msi installers are actually just a wrapped NSIS installer, do you think it would be simple enough to make a script to do this?

[Trihedraf]

First installer I've ever made, let alone trying extra stuff. This was just in CMake already, so I was able to make it spit it out with reasonably small changes and decent result. I could look into it at some point though.

[AJenbo]

That would be really helpful. I'm all for providing an installer, but unfortunately a lot of AV will prevent users from downloading .exe files but will allow .msi so that is what prevents us from using NSIS for it. Additionally it's only possible to generate MSI installers on Windows (using the WIX generator in CPack).

Update: After some digging it turns out that WIX is only even build for CPack on Windows platforms, so we would need to invoke it externally even if we manage to install WiX via Wine.