Rework code and add some more features.

Add overall state to service manager.
Pull in current service configuration on startup (username and iTunes path).
Fix crash on errors during service install / uninstall.
Launch iTunes under cached service user credentials and only when user validated by service being installed. Closes #4.
Improve feedback on failed install / uninstall tasks.
Added build events to automatically stop service when building and restarting if was previously running.