Add InnoSetup Packager for Windows.

Modeled after the NullsoftInstallerPackager, so hopefully compatible for most simple cases, but not for registry keys. I have added some more hands-on support for file associations.

An MR to add a blue print for InnoSetup is here: craft-blueprints-kde!386 (merged)

This really an alternative to !71 (closed) . InnoSetup has multi-threaded lzma/lzma2 compression built into it, and even allows for some finetuning of compression.

While for the time being, this installer could co-exist with the NSIS one, I believe it will also be more maintainable in the long run, and should replace it, eventually. (At least, personally, I never became friends with NSIS syntax).