Implement lazy loading of images

[WSydnA]

Perceived performance is quite poor on slow connections or low-powered devices due to the number of images being loaded. Lazy-loading should be introduced so images are only loaded if they are in the current viewport.

Placeholders/loaders should be used while images are downloading.

In the details view, the image container should have a fixed height prior to the image downloading, to avoid a flat (but still bordered) container.