Add support for non-apple keyboards

[edualm]

Hey,

I use a non-apple keyboard on my mac. Even though it's a mac keyboard (has all the keys that the others have on the same spot), I have found that the media keys work under iTunes but not under other apps like Spotify (only the play/pause does, not the forward and rewind ones).

After some testing that I have found that on my keyboard the key codes 17 and 18 are applied to ffwd and rewind, respectively. Since it works under iTunes, I don't think it would be a bad idea to add support for these key codes here, as I am mostlikely not the only one that suffers from this issue.

I may also be able to implement it. Just give me your oppinion on this matter.