1. fix bug in clustering. 2.adapt gp demo to new

1. fix bug in clustering. 
2.adapt gp demo to new GaussianProcessRegression class. 
3. user now can choose kernel_function in gp demo. 
4. rewrite the kernel_matrix visualization demo in new framework, but got a defective result. I'll check if there's any better way than conrec.js for heatmap drawing, or else I'll fix the defect.
5.data_importer still need some time to finish, I'll send a pr once I finish it.