Support preserveAspectRatio for image elements

Currently in SVGKit preserveAspectRatio is supported for &lt;svg&gt; elements but not for &lt;image&gt; elements. This pull request adds support for supporting preserveAspectRatio for raster images in &lt;image&gt; elements. It even supports the "slice" option which the &lt;svg&gt; support for preserveAspectRatio doesn't support.
It's not really needed; I'll remove.

On Aug 13, 2014, at 3:19 PM, adamgit <notifications@github.com> wrote:

> In Source/DOM classes/SVG-DOM/SVGFitToViewBox.h:
> 
> > @@ -19,4 +19,7 @@
> >  
> >  @property(nonatomic,retain) SVGAnimatedPreserveAspectRatio* preserveAspectRatio;
> >  
> > +-(double)aspectRatioFromWidthPerHeight;
> > +-(double)aspectRatioFromViewBox;
> This interface is defined by the spec. We cannot add to it.
> 
> If you need to add new methods, you'll need to create a custom class and/or extension header (that does NOT begin with the letters "SVG"; it can begin with "SVGK" instead)
> 
> —
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