Conditionally compile plugins based on platform

[joeGraf]

You specify the platforms in the .uplugin file. Like so:

"Modules" :
[
    {
        "Name": "FlurryEditor",
        "Type": "Editor"
    },
	{
		"Name" : "IOSFlurry",
		"Type" : "Runtime",
		"LoadingPhase" : "PreDefault",
		"WhitelistPlatforms" : [ "IOS" ]
	}
]