Come up with a better way to reference dynamic icon values

[jordanbyron]

Currently anytime Apple releases a new set of UIApplicationShortcutIconType icons we have to manually update our corresponding dictionnary which maps a string value to the enum value. This is stinky and I'd love to come up with a more elegant solution, less manual solution.

Ref: #26
https://github.com/madriska/react-native-quick-actions/blob/master/RNQuickAction/RNQuickAction/RNQuickActionManager.m#L61