Make the Source and Graph frames resizeable

[asteiner-psh]

...by dragging the edge between the two frames.

[magjac]

Sorry for the delay and thanks for the suggestion. I agree that that would be useful.

[magjac]

@asteiner-psh Not exactly what you suggested, but I've added a fullscreen (within the browser window) mode for the graph. You can try it at http://magjac.com/test/graphviz-visual-editor/.