remove @shadow instances and replace with escaped values, update mixins to not use a default value at all

Added the back-face visibility css property to mixins.less, this property prevents the browser flickered experienced especially in Chrome when using 3D transformations.

1. Removed borders on .btn and increased line-height 2px to compensate
2. Set buttons to use the endColor of the gradient as the background-color by default for extra contrast between button and background
3. Set a 5% darker background-color on hover of buttons just for IE7

fix other instances of mixins, swap use of box-shadow everywhere, include border-radius and transition

The native box-shadow, background-clip and background-size instructions all take 1 or more arguments. In 1.3.0 LESS became arity aware, see https://gist.github.com/1933613. As a result the signatures of these mixins had to change a little.

in responsive layouts <767px, ensure inputs are not larger than 100% with box-sizing and a max-width

restore fixed navbar container reset to grid mixin, add override for inputs within grid mixins to fix #2080

rewrite the grid system. Clean shit up tons - only generate 12 columns by default - custom builder will do differently if you request it.

set width to auto for default navbar container, then override it later for fixed navbars (done all via the #gridSystem mixins)