Add categories.properties for book categories

Signed-off-by: Pekka Helenius <fincer89@hotmail.com>

bookstore/src/main/resources/categories.properties

@@ -0,0 +1,15 @@
+# Pekka Helenius <fincer89@hotmail.com>, Fjordtek 2020
+
+# NOTE:
+#   These properties represent internal application properties,
+#   NOT linguistic front-end message strings. Never refer to keys
+#   in this file in your application front-end messages.
+#   These keys are accessible in Spring Environment context.
+
+
+
+# Bookstore category properties
+#
+bookstore.category.fantasy = Fantasy
+bookstore.category.horror  = Horror
+bookstore.category.scifi   = Sci-Fi