Add confirmation dialog for eject key

[Linus Bobcat]

I'm running elementaryOS Luna on a non-Mac computer but I use a Mac keyboard that has an eject key. I found that sometimes I would accidently hit it. This is not much of a problem for me, because I don't have a DVD/CD drive and the only thing that happens is that I see a notification that notifies me that I pressed the key but I have tested it and it does indeed try to eject any media. As for people who use DVD/CD drives I think this would be a problem. My proposed solution is to replicate OS X' behaviour and make it so that the eject key has to be held for a few seconds in order for the dvd/cd to be ejected so users won't accidently eject their DVD/CDs