Implement all keywords for polynomial_chaos and stoch_collocation methods

I've implemented a minimum set of keywords that allow these methods to work. For completeness, all the keywords available for [polynomial_chaos](https://dakota.sandia.gov//sites/default/files/docs/6.4/html-ref/method-polynomial_chaos.html) and [stoch_collocation](https://dakota.sandia.gov//sites/default/files/docs/6.4/html-ref/method-stoch_collocation.html) should be implemented.
