Added support for Images from URL,Supply any type

[bensalcie]

This PR has fixes to enable one load images from a URL without doing anything on flutter. Just supply the corresponding URL . If it starts with http/https it will be loaded from online. If not, it will loaded from Assets.This has the update to load the images asynchronous, so you don't have to worry about Blocking UI to your flutter App.

1. Maintain default convinience extension. (FCPExtensions.swift)

convenience init?(withURL url: URL) throws {
                  let imageData = try Data(contentsOf: url)
                  self.init(data: imageData)
                }

2. When about to render image, check the source. Then dispatch it on a separate thread for both local and url images.

if image != nil {
             if image!.starts(with: "http"){
                 DispatchQueue.global(qos: .background).async {
                     let url = URL(string: self.image!)
                     let stationImage = try? UIImage(withURL: url!)
         //
                         DispatchQueue.main.async {
                             listItem.setImage(stationImage)
                               }
                       }
             }else{
                 listItem.setImage(UIImage().fromFlutterAsset(name: image!))
             }
         }

This will intercept all urls beginning with http with custom loader and those beginning with any other format as asset images.
Thank you.

[oguzhnatly]

Thank you for your contribution @vanlooverenkoen!
I'm testing on real devices and cars as well. Once it's done, I will be approving and merge the changes as soon as possible.

[vanlooverenkoen]

Duplicate of #24

[bensalcie]

Implementation is bit different. We can test for both and see any performance issues. I tried your approach and when #24 inside Isolates, I get some lag. I had to go the approach on the last commit. But my view is relative.

[larry-cariq]

Hi @oguzhnatly. This is a very nice package and very useful. Are you thinking about merging this PR and releasing a package update? Just curious if I should wait for the update or fork and build it myself. Thanks.