Add MetaType.Numeric

Closes #80 (closed)

arkindex_worker/worker/metadata.py

@@ -12,6 +12,7 @@ class MetaType(Enum):
     Location = "location"
     # Element's original structure reference (intended to be indexed)
     Reference = "reference"
+    Numeric = "numeric"
 
 
 class MetaDataMixin(object):