Parameter interpolation of model templates with a single 4D RBF model

Attempt to make parameter interpolations of stellar model templates using a single 4D radial basis function (RBF) which is modeled over all the original model templates. 

The 4D RBF interpolations using neighboring model templates reproduce model spectra with high quality (<1%) as reported in PIPE2D-460 but the processes are time-consuming because RBF models are generated at every parameter grid. In this ticket, we try to reduce the processing time by using only a single RBF.