Add SVG attributes needed for (X)HTML resizing

Currently, if you just load a saved SVG file in a web browser (ie, Firefox 3), the image is not resizeable/scalable. If you change the width/height of the object in the <object> tag, then the image is just cropped and scrollbars added. However, two simple attributes added to the <svg> tag of the file allow the browser to have full control over the image and rescale it as you would expect. Ideally, some sort of UI options in the document preferences could be available to set the preserveAspectRatio (or just do via XML editor if need be). Or, if these attribs have some negative effect on overall operation of inkscape, add a "save for web" option that adds them by default (and fits the page to objects).

Example for good defaults:
<svg>
   ... other attribs...
   preserveAspectRatio="xMinYMin meet"
   viewBox="0 0 {width} {height}"
   ... other attribs ...
</svg>

References:
http://www.w3.org/TR/SVG/coords.html#PreserveAspectRatioAttribute
http://www.w3.org/TR/SVG/coords.html#ViewBoxAttribute

The width attribute on the outermost 'svg' element establishes the viewport's width, unless the following conditions are met:

    * the SVG content is a separately stored resource that is embedded by reference (such as the 'object' element in [XHTML]), or the SVG content is embedded inline within a containing document;
    * and the referencing element or containing document is styled using CSS [CSS2] or XSL [XSL];
    * and there are CSS-compatible positioning properties [ CSS2-POSN] specified on the referencing element (e.g., the 'object' element) or on the containing document's outermost 'svg' element that are sufficient to establish the width of the viewport.