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.