Add LaunchWorkingDir to wixstdba to facilitate processes that require a different working folder

[WIXBUG:3750](http://wixtoolset.org/issues/3750/)
Separate pull request created for wix4
It's true, I didn't give any way in LaunchApprovedExe to specify the working folder.  On the plus side, LaunchApprovedExe already sets the working folder to the exe's folder.