Fixing IE10 issues with lazy load

IE10 returns undefined for naturalWidth until the image supplied in the src has loaded, rather than the 0 defined in the spec. The 'naturalWidth' in (new Image) gets around this.

It also adds a width and height to the lazy loaded images, that the this.gif.removeAttribute fix further up doesn't fix. I've removed the attributes again once the image has had its src swapped and this fixes the issue.

Lazy Loading now works perfectly in IE10!
Imager.getNaturalWidth unit test.

The function is now a public static method to get proper test coverage as it is quite critical to detect images width.
Try a more bulletproof approach.
Compute natural width after image is loaded.
Remove CI timeouts as they are pretty much useless now tests are run over BS.
Timeout setup for `getNaturalWidth` unit test.
Merge pull request #105 from BBC-News/fix-99

Imager.getNaturalWidth(image)