Kill spawned processes when Spectrum is closed

[Ashoat]

Currently, Spectrum can be closed in a way that causes its child processes to be orphaned. It's possible to add code that makes sure that the child processes get closed when the MainWindow is closed, but that won't address the case where Spectrum is closed because of a kill signal or a crash. Hitting the stop button in Visual Studio issues a kill signal, which means if we want to handle that correctly we'll need to address this issue.

Doing this correctly requires some weird Windows kernel stuff. This StackOverflow answer has the details.