Moved reusing extensions to separate file

bookshop/srv/admin-service.cds

@@ -1,5 +1,4 @@
 using { sap.capire.bookshop as my } from '../db/schema';
-
 service AdminService @(_requires:'authenticated-user') {
   entity Books as projection on my.Books;
   entity Authors as projection on my.Authors;

bookshop/srv/cat-service.cds

@@ -1,5 +1,4 @@
 using { sap.capire.bookshop as my } from '../db/schema';
-
 service CatalogService @(path:'/browse') {
 
   @readonly entity Books as SELECT from my.Books {*,
@@ -8,8 +7,4 @@ service CatalogService @(path:'/browse') {
 
   @requires_: 'authenticated-user'
   action order (book : Books.ID, amount: Integer);
-
 }
-
-// activate pre-build extensions from...
-using from '@capire/common';

bookshop/srv/ext.cds

@@ -0,0 +1,2 @@
+// Incorporate pre-build extensions from...
+using from '@capire/common';