Support custom remote photo item classes

[flambert]

Example: To use something else than SDWebImage to download the image

[ethan605]

Hi Francois, I'm very interested with your idea of replacing SDWebImage by something more flexible. But after a while of inspecting your pull request, I still don't get your idea. Can you update the Readme markdown to explain more how to use this?

[flambert]

Hi,

It's kind of really back-ended and hacky.
The more I think about it, the less I like it.

I'll update the readme with an example on how to use it, but I'll still try to come up with better solution (I was kind of in a hurry when I wrote that code).

I vaguely remember coming up with it because the customView would not update the maximumZoomScale of its containing view.

So maybe simply adding a protocol for the local/remote/custom view to set the containing UIPhotoItemView and maybe make a base implementation (or another protocol) for the remote view would be simpler to use.

[ethan605]

Thanks for your quick reply. I like your idea and I think you could resolve it best. Take your time and make it as good as you want :)

Also, I've updated (actually merged) your other pull requests, which leads to conflicts in this request. Please merge the latest codes to your branch for resolving conflicts. Thanks so much :)