Update Masonry from 2.1.08 to 3.1.0; add imagesLoaded and jquery.debouncedresize plugins.

This is a rather huge change as Masonry 3 drops support for jQuery animations (directly affecting IE8 and also IE9).
Also, both imagesLoaded and jquery.smartresize are not part of Masonry anymore and thus are now included in plugins.js.

Very smooth update, thanks @desandro!
Update readme.
Fix hidpi-logo (adjust to imagesLoaded v3).
Merge branch 'feature/update-to-masonry-v3' into develop