[VUFIND-1718] minor updates to LC class/subclass to subject label map…

…ping (#4055)

This patch adds a label for class "A" and disambiguates the labels
for "C" and "D".

import/translation_maps/callnumber_subject_map.properties

@@ -1,3 +1,4 @@
+A = A - General Works
 AC = AC - Collections and Collected Works
 AE = AE - Encyclopedias
 AG = AG - Dictionaries and Reference
@@ -23,7 +24,7 @@ BS = BS - The Bible
 BT = BT - Doctrinal Theology
 BV = BV - Practical Theology
 BX = BX - Christian Denominations
-C = C - General History
+C = C - Historical Sciences
 CB = CB - History of Civilization
 CC = CC - Archaeology
 CD = CD - Diplomatics, Archives, Seals