add ability to load BEEF correlations for UQ

Author: sevyharris

rmgpy/tools/uncertainty.py

@@ -57,6 +57,7 @@ def __init__(self, dG_library=1.5, dG_QM=3.0, dG_GAV=1.5, dG_group=0.7159, dG_AD
         self.dG_group = dG_group
         self.dG_ADS_correction = dG_ADS_correction
         self.dG_surf_lib = dG_surf_lib
+        self.library_covariances = None  # placeholder to allow future covariance
 
     def get_uncertainty_value(self, source):
         """