Hide loading animation after media has been loaded

Showing the animation looks realy annoying behind smaller images or images with transparent parts.
adjusted swipebox.scss according commit "Hide loading animation after media has been loaded(...)" f95c6d0128dd108b7a034126bbb3d5dca13fc4b9
Merge pull request #147 from stackcoder/pull-request-loading-animation

Hide loading animation after media has been loaded