Included jquery-unveil library for lazy image loading.

For more about the library:

http://luis-almeida.github.io/unveil/
WIP: lazy loading images in entries.
Upgraded angularJS from 1.2.10 to 1.2.13
WIP: add data-src attribute to attributes whitelist in angularJS html sanitization.

This is intended to allow the user of jquery-unveil library for lazy image loading; this plugin needs a data-src attribute to be added to images, and this attribute is currently being removed by angularJS anti-xss sanitization for the ng-bind-html directive.
Revert "WIP: add data-src attribute to attributes whitelist in angularJS html sanitization."

This reverts commit 962d28f193803a85327188f2cb47ad762b615325.
Mark entry contents and summaries as explicitly trusted when binding them into the AngularJS view.

This is necessary because by default the ng-bind-html directive removes the data-src attribute from images in entries; this attribute is necessary for the jquery-unveil library (for image lazy-loading) to work. Explicitly marking the html in entry summaries and contents as trusted, it is inserted in the view without modifications.
WIP: lazy loading images.

It's starting to look like the best option is to implement this in an angular service, instead of using js libraries. This would allow other functionalities to be added (adding a class with margins and display-block only if the image is big enough, try to load the image as a relative URL in the feed server if the first attempt to load it fails).

Not yet implemented:

- remove all traces of jquery-unveil library (no longer used)
- move lazy-loading code to its own angularjs service
- implement the above additional features
- implement a lazy-loading solution when user has requested all entries to be open by default
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.
Acceptance tests for lazy-loading entry images.
Acceptance test: images not prepared for lazy-loading in entry contents or summaries are displayed correctly.
Moved code for image lazy loading to a separate angularjs service.

This code currently only works when entries are closed by default (the default configuration).
Lazy load images after actually opening the entry.
Replaced the Hint.css library with Bootstrap tooltips.

A new angularjs service has been added to enable tooltips as necessary (bootstrap tooltips are disabled by default and must be enabed via javascript).

This should solve performance problems with Hint.css after implementing lazy image loading.
Remove margins from "mark as read" and "mark as unread" buttons in the entry toolbar.

Bootstrap by default gives a 5px margin-left to the second and successive buttons in a toolbar. We are showing only one button at once, which meant that the button that appeared first in the markup was displayed with no margin-left, and the second one was displayed with a small margin-left. The visual effect was that the button "jumped" a bit to the left or right when clicking.

The fix is to remove margins for those buttons. This will probably require some refining when more buttons are added (e.g. social sharing).
Added shadow under the navbar.