Some jQuery helpers & less mixins

Added some helpers to plugins.js ($.scrollPage, $.getDocHeight,
$.cookie, $.getCookie, $.clearCookie).
Also added a few mixins to mixins.less (Notably reset, topRight, shadow,
text-shadow, ie8-shadow, removeShadow, borderImageGradient,
gradientWithImage, gradientStops, breakInside, breakAvoid,
transform-origin, transition-prefix, column-span).

With these mixins you can do more with gradients, and skip the ie<9
shadows if you don't want them in your code.
JQuery Helpers and more LESS mixins