[TIMOB-25210] iOS: Cannot submit builds with iOS 11 / Xcode 9 due to missing "Marketing Image"

I just received feedback from Slack that you currently cannot submit any iOS 11 app due to the error "Missing Marketing Icon - iOS Apps must include a 1024x1024px Marketing Icon in PNG format. Apps that do not include the Marketing Icon cannot be submitted for App Review or Beta App Review.". The issue simply occurs because Apple introduced a new Icon-type in the asset-catalog called "iOS Marketing", which represents a 1024x1024 PNG image. As we already have our DefaultIcon.png, the SDK change would simply grab it and reference the new key in the asset-catalog. Also, we should now enforce the users to specify a "DefaultIcon.png" for iOS 11 distributions and deprecate the manual appicon.png formats. Also see [this Stackoverflow thread](https://stackoverflow.com/questions/44565883/missing-marketing-icon) for more context. *EDIT*: Required asset-catalog object to add:

 {
      "size" : "1024x1024",
      "idiom" : "ios-marketing",
      "filename" : "DefaultIcon.png",
      "scale" : "1x"
}

*EDIT 2*: The following change in our _build.js could allow the app-icon to be received via "appicon-Marketing.png":

'-Marketing':     { height: 1024, width: 1024, scale: 1, idioms: [ 'ios-marketing' ], minXcodeVer: '9.0' }

The same would probably need to be done for the DefaultIcon.png, so we won't need to deprecate anything, yet, just make sure it's supported for both DefaultIcon, non-DefaultIcon, asset-catalog and non-asset-catalog. *EDIT 3*: The above change seems to work (although some others are still missing, might be interesting to investigate later): !Bildschirmfoto 2017-08-30 um 12.19.41.png|thumbnail!