JGraphX: label rotation support

[VsevolodGolovanov]

mxConstants.STYLE_ROTATION in JGraphX affects shapes, but not their labels. Should affect labels too, as it does in mxGraph.

[VsevolodGolovanov]

I've been looking into implementing this. Obviously the painting code needs to be updated in mxDefaultTextShape and mxHtmlTextShape.
Secondarily, mxUtils.getScaledLabelBounds, mxGraph.getPreferredSizeForCell and mxGraphView.getWordWrapWidth should take rotation into account. Is that it?

[davidjgraph]

Unfortunately, we don't actively develop JGraphX, we closed down the issue tracker in that project for this reason.

[VsevolodGolovanov]

I suggest updating jgraphx/README.md to reflect its current status.

[davidjgraph]

Done.