Add layer to perform RBF interpolation in reduced order modeling (#315)

* add RBF implementation in pytorch (in layers)
* add POD-RBF example (baseline for nonintrusive closure)
* Add POD only and POD+RBF implementation
* add POD-RBF in tutorial 8

docs/source/_rst/_tutorial.rst

@@ -43,4 +43,4 @@ Supervised Learning
    :titlesonly:
 
    Unstructured convolutional autoencoder via continuous convolution<tutorials/tutorial4/tutorial.rst>
-   POD-NN for reduced order modeling<tutorials/tutorial8/tutorial.rst>
+   POD-RBF and POD-NN for reduced order modeling<tutorials/tutorial8/tutorial.rst>