Avoid central index.cds files to ease extensibility

fiori/app/admin/fiori-service.cds

@@ -1,4 +1,4 @@
-using { AdminService } from '../../db';
+using { AdminService } from '../../db/schema';
 
 ////////////////////////////////////////////////////////////////////////////
 //

fiori/db/hana/index.cds

@@ -2,7 +2,7 @@
 //  Add Author.age and .lifetime with a DB-specific function
 //
 
-using { AdminService } from '..';
+using { AdminService } from '../schema';
 
 extend projection AdminService.Authors with {
   YEARS_BETWEEN(dateOfBirth, dateOfDeath)         as age: Integer,

fiori/db/sqlite/index.cds

@@ -2,7 +2,7 @@
 //  Add Author.age and .lifetime with a DB-specific function
 //
 
-using { AdminService } from '..';
+using { AdminService } from '../schema';
 
 extend projection AdminService.Authors with {
   strftime('%Y',dateOfDeath)-strftime('%Y',dateOfBirth)              as age: Integer,