Refactor db parts

fiori/db/common.cds

@@ -0,0 +1,14 @@
+namespace sap.capire.bookshop;
+
+using { sap.capire.bookshop } from '@capire/bookstore/srv/mashup';
+
+entity GenreHierarchy : bookshop.Genres {
+  hierarchyLevel : Integer default 0;
+  drillState     : String default 'leaf';
+  parent         : Association to GenreHierarchy;
+  children       : Composition of many GenreHierarchy on children.parent = $self;
+}
+
+extend service CatalogService with {
+  @readonly entity GenreHierarchy as projection on bookshop.GenreHierarchy;
+}