Close when queue finishes

[vertigo220]

Just tested to see what happens when trying to close RZ during an update, and found it tells you doing so will abort the install(s), which appears to be due to issue #86. How about taking it a step further, though, and providing an option to close when done? To be clear, this would only be if you click the close button and select the option it would provide in the pop-up warning, not anytime the queue finishes.