Minor cleanup - EditFileEventArgs

I was going to wait until I implemented something more substantial to merge this in, but since I'm rather busy with my own projects right now and haven't found any more bugs to fix (I guess that means I'm doing my job!), nor do I have any ideas for new features, I'll do it now.

Basically all this is is renaming properties of EditFileEventArgs to not only make the names less verbose, but also closer to what's "normal" for .NET.  'IsAlreadyMatched' was way too long a name and most other WinForms events with such a property call it simply 'Handled', so I followed suit. :smile: 'FileFullPath' is simply Path, and 'FileExtension' is just 'Extension'.