WKWebView support

[manucorporat]

ionic-team/cordova-plugin-wkwebview-engine#46
To keep track of the progress.

WKWebview does not use NSURLProtocol under the hood so the current approach to allow self-signed certificates does not work.

Fortunately there is a way:
http://stackoverflow.com/questions/27100540/allow-unverified-ssl-certificates-in-wkwebview/32507262#32507262

(only iOS9)

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[hypery2k]

idea would be to add to specify webview as an argument sent to the plugin as there are ways of determining the webview in use on the javascript side. This could also potentially deal with incorporating crosswalk support as the dev should be able to specify and then the native component doesn't have to detect and switch automatically.