Optimize SVG and XGMML output

[proost]

Now data is added to the cytoscape object, exported to json, loaded into a has and rendered again.

With the updated renderedStyle() the elements can be rendered directly, this should speed up the function considerably.

As this function takes some time to finish the browser sometimes wishes to kill the script. Ideally this can be avoided !

[proost]

xgmml done: b6a473a

[proost]

xgmml fixed and svg done : 554ca84