fix bug in clustering.
2.adapt gp demo to new GaussianProcessRegression class.
user now can choose kernel_function in gp demo.
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.