Implement new dimension param helpers

===Element Dimensions Definitions===

box     = margin + border + padding + content
visual  = box - margin
client  = visual - border
content = client - padding

Box refers to box model dimensions definition: http://www.w3.org/TR/CSS2/box.html

Visual refers to the offset dimensions specified by the MS DHTML object model: https://developer.mozilla.org/en/DOM/element.offsetWidth

Content refers the the content section in the box model definition.

element#getDimensions(String preset | Object options) -> { width: number, height: number }

presets = box, visual, client, content
options = { margin: true, border: true, padding: true }

element#getDimensions() -> Defaults to "visual"

element#getDimensions({ margin: true, border: true, padding: true }) -> returns Object representing box preset
element#getDimensions({ margin: false, border: true, padding: true }) -> returns Object representing visual preset
element#getDimensions({ margin: false, border: false, padding: true }) -> returns Object representing client preset
element#getDimensions({ margin: false, border: false, padding: false }) -> returns Object representing content preset