Nuke 10.3.1

Added Xamarin.Nuke (https://github.com/roubachof/NukeProxy) nuget package as dependency, bump to Nuke 10.3.1.
All of this thanks to the one and only @Cheesebaron.

Fix handling of Gif

Fix issue #17 Gif not works on iOS

Remove SwiftRuntimeSupport from dependencies

Support for iOS < 12.2

As specified here: https://docs.microsoft.com/en-us/xamarin/ios/platform/binding-swift/walkthrough#consume-the-binding-library

You need to add the Xamarin.iOS.SwiftRuntimeSupport NuGet package to your target project if you want to support iOS 12.1 and earlier.
Please read the above doc to submit an app with such support.

Fix `FileImageSource` Handling

Fixes #12 #3 #8 #9 #11
By changing the way Nuke is handling images with a FileImageSource.

Xamarin.Forms.Nuke cannot cache images coming from the Asset Catalog:

https://docs.microsoft.com/en-us/xamarin/ios/app-fundamentals/images-icons/displaying-an-image

This is due to the fact that the Asset Catalogue is packed in the ipa, and you cannot get an image URI from it.
Since version 8.4.1, it will however cache correctly images respecting the density convention (@2x, @3x) locating in your Resources folder (see Issue #13).

However, if you still have some issues with your local images, you can disable Xamarin.Forms.Nuke for all FileImageSource by setting the disableFileImageSourceHandling parameter of the FormsHandler.Init to true:

Xamarin.Forms.Forms.Init();
Xamarin.Forms.Nuke.FormsHandler.Init(debug: false, disableFileImageSourceHandling: true);
LoadApplication(new App());