New Clustering Demo

[zhengyang92]

1. Add a clustering demo, the link is "http://shogun-toolbox.org/demo/clustering/entrance"
2. Add security check for exceptional input.
3. fix the bug that the mouse can click outside the coordinate system.
4. fix the range of the x-axis to 0..1 and adjust the parameter of the svr demo.
5. small changes on the dot style and fix the page-title of svr demo.
6. I'll add some animation on the curve in next version.