Adds extra_uninstall_flags option for windows packages

To handle automated uninstalls where settings files are required like for uninstallation, like with InstallShield.

InstallShield requires you to generate an automated uninstall settings by running through the uninstaller.  This can be  installation specific rather than package specific, so they need to be supplied in the state file, rather than the package repository.  This mirrors the extra_install_flags option.