Gradient fix

Added rendering of gradientTransform, fixed gradient position ( not working since big commit of svg import ) fixed use of xlink:href in gradients, stop opacity 0% was omitted. Fixed toSVG for gradients.
Added gradients for stroke property.

Related to issue #1597
we need null check. opacity at 0 was returning false and was not exported.
so it was default 1.
Il 16/ago/2014 15:08 "Juriy Zaytsev" <notifications@github.com> ha scritto:

> In src/gradient.class.js:
>
> > @@ -202,13 +209,13 @@
> >            '<stop ',
> >              'offset="', (this.colorStops[i].offset * 100) + '%',
> >              '" style="stop-color:', this.colorStops[i].color,
> > -            (this.colorStops[i].opacity ? ';stop-opacity: ' + this.colorStops[i].opacity : ';'),
> > -          '"/>'
> > +            (this.colorStops[i].opacity != null ? ';stop-opacity: ' + this.colorStops[i].opacity : ';'),
>
> Do we need != null check or could simple ! be enough here?
>
> —
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> <https://github.com/kangax/fabric.js/pull/1598/files#r16324690>.
>