[iOS] Add json arguments and "MusicControls" keyword

[homerours]

Add support for json arguments in the iOS functions (on the androidWindows branch). Maybe use "MusicControls" keyword instead of RemoteControls: it's more precise.
Also implement the "music-controls-********" messages on iOS.

[shi11]

Remote-Controls keyword is what Apple uses as it extends beyond music into other Media types and scenarios.
see: https://developer.apple.com/library/ios/documentation/EventHandling/Conceptual/EventHandlingiPhoneOS/Remote-ControlEvents/Remote-ControlEvents.html

[homerours]

Ok. Sorry for this, I don't know anything about iOS.

[shi11]

That's why we'll work well together - I don't know anything about android or windows :)

[homerours]

@filfat You're absolutlely right and if you want to contribute, you're welcome ;)