Lazy loadding support

[tejadong]

Hi guys:

I think it would be convenient to integrate or add as a requirement the package https://github.com/tjoskar/ng-lazyload-image this library because I tried to load 100 images and the component takes a long time to load.

I've been looking at the structure of ionic-gallery-modal and I think it would only be necessary to replace the src tag of the fitted-image component with that of [lazyLoad] loading and I think it should be working fine.

Thanks. Great component.