WiX/MSI setup project

- create MinionMSI WiX project
- create MinionConfigurationExtension extension library
- remove pkg/windows/installer
- move pkg/windows/buildenv into MinionMSI
- simple msbuild project to restore dependencies and build the setup
  package.

See README.md for more details.

Should address #19137, #14806, #12187, #4633, #4614, #4502 and #4136.
Provides a starting point for #19220, #18412, #18431 and #12804.
May resolve #19232.

NOTE 1: I've only tested install/uninstall on my own machine (Win7 x64 SP1) with a win32 build.

NOTE 2: This does not implement the vcredist install and cannot cleanly uninstall if the minion service is running. These appear to be limitations of .msi; the former could be fixed by a bundle install or (preferably) inclusion of the vc++ 2008 redist merge module, the latter by removing nssm.exe altogether.