Updated Jgraph to 1.12.0.0

- Fixes output of mxUtils.getXml for Firefox 20 [JavaScript]
- Fixes child offset for swimlanes in mxStackLayout [JavaScript]
- Moves setting zIndex for tooltips in mxTooltipHandler from init to show [JavaScript]
- Adds startEdit, endEdit and executed events in mxGraphModel, mxUndoableEdit [JavaScript]
- Fixes undefined roots variable usage in hierarchical layout [JavaScript]