Hide loading animation after media has been loaded

Showing the animation looks realy annoying behind smaller images or images with transparent parts.
Try to extract caption also form alt attribute of an included image

At this time we needed to specify the title attribute and the alt attribute redundant.
Clicking on a loaded image switches to the next image, clicking on the background overlay closes the swipebox

I think this behaviour is known and expected by most of the users (especially when using a non default transparent skin).
This shouldn't affect any touch devices.