Various fixes

This commit propose :

Viewbox support ( with translating and scaling effect proper of viewbox, not yet supported in fabric js)
path, polygon, line, polyline position fixes added to support new scaling and translating effect of viewbox
( consider that now any svg imported will have nested transformation if it has a viewbox )
text stroke fixes, text anchor fixes and Text position fixes for errors showed up after 1.4.8
All the assets i have test render correctly ( pixel perfect to my eyes ) except the one having text inside ( font issue, width and height calculation of text with differents fonts ) and execpt the one having widht and height unspecified or at 100% or features supported partially ( stylesheet parsing, effects like blur )

Please check it in action at:
http://www.deltalink.it/andreab/fabric/a.html

vs current fabricjs in 
http://www.deltalink.it/andreab/fabric/b.html