updates to Graizer 18 GMM

second attempt to implement, still incomplete. GMM enum included for testing in response spectra tool

See #123 (closed)

src/main/java/gov/usgs/earthquake/nshmp/gmm/Gmm.java

@@ -250,12 +250,12 @@ public enum Gmm {
       SadighEtAl_1997.COEFFS_BC_HI,
       SadighEtAl_1997.CONSTRAINTS),
 
-  // /** @see Grazier_2018 */
-  // GRAIZER_2018(
-  // Graizer_2018.class,
-  // Graizer_2018.NAME,
-  // Graizer_2018.COEFFS,
-  // Graizer_2018.CONSTRAINTS),
+  /** @see Grazier_2018 */
+  GRAIZER_2018(
+      Graizer_2018.class,
+      Graizer_2018.NAME,
+      Graizer_2018.COEFFS,
+      Graizer_2018.CONSTRAINTS),
 
   /* Subduction Interface and Slab WUS 2008 2014 2018, AK 2007 */