Add support for olderThan parameter

[RalfNieuwenhuizen]

This parameter works the same as "after" parameter in react-native CameraRoll (https://facebook.github.io/react-native/docs/cameraroll.html)

[olofd]

Great PR. Will merge

[CrazyPython]

@RalfNieuwenhuizen Hi, I was working on a newerThan parameter, and I'm having some trouble. How is olderThan passed in from the JS side?

[RalfNieuwenhuizen]

@CrazyPython it's the timestamp of the previous photo, in string format. Passed in in the fetchOptions like this:

const images = await RNPhotosFramework.getAssets({
        fetchOptions: {
            olderThan,
            fetchLimit,
            mediaTypes: ["image"],
            sourceTypes: ["userLibrary", "cloudShared", "itunesSynced"],
            sortDescriptors: [
                {
                    key: "creationDate",
                    ascending: false,
                }
            ]
        },
        includeMetadata: true,
        includeResourcesMetadata: true,
    });