Button to set resolution based on source window resolution

I found myself changing the resolution a lot when streaming small windows, so I added a button to the source window to set the resolution to match the selected window.  This does not call ResizeWindow because the function is private (if you decide this button is worthwhile you can decide to make it public or what).

I also edited the .rc file by hand.  I don't usually do Windows stuff so I'm not sure if I should have done it some other way.