Photo_view: Adding to List of PhotoViewGalleryPageOptions

[dandansoysauce]

setState() called after dispose() is being thrown when I'm trying to add an item to a List<PhotoViewGalleryPageOptions>

My Setup:

return PhotoViewGallery(
  pageOptions: List<PhotoViewGalleryPageOptions>
);

And I'm doing setState() on every page change - onPageChanged()

[renancaraujo]

I think we should use a builder pattern instead of a list.

[renancaraujo]

Added the builder constructor on #119 and published in the version 0.2.3.