Test SVG EXPORT

This is a preliminary work, nearly done for the svg export.
Final PR will have clean files, those commits are dirty.

@kangax if you can help me with the 2 failing tests, from polygon and polyline, i searche all fabric.js file and there is no trace of that error in case of missing points.
I even searched on past revision, but it looks like that function never existed.

I'm commenting some lines to explain you some decisions.
if it is top left as default, i will render it as top left. so the center is left + radius, top + radius.
global alpha moved in object class.
No need to tweak top and left when we parse from element.