Removed jquery-unveil JS library.

Lazy loading of images will be achieved with a custom angularjs service.
When saving entries, the src of each image is copied to a data-src attribute, and the src URL is replaced with that of an animaged spinner gif.

The animated gif is a Creative Commons-licensed image from wikimedia:

http://commons.wikimedia.org/wiki/File:Ajax-loader.gif
Lazy-load images only if they have a data-src attribute.

This is intended so that old entries (saved before implementing lazy load, which images do not have a data-src attribute) are displayed correctly.
The angularjs controller method that returns trusted HTML for entry contents works better in the cases in which the entry does not have either a summary or a content attribute.
Unit test for Entry model tests that images are modified to support lazy loading.
Acceptance tests stubs for image lazy loading feature.