Added the Services layer to the code to do the database operation

src/pilgrim/service/servicemanager.py

@@ -0,0 +1,19 @@
+from pilgrim.service.entry_service import EntryService
+from pilgrim.service.travel_diary_service import TravelDiaryService
+
+
+class ServiceManager:
+    def __init__(self):
+        self.session = None
+    def set_session(self, session):
+        self.session = session
+    def get_session(self):
+        return self.session
+    def get_entry_service(self):
+        if self.session is not None:
+            return EntryService(self.session)
+        return None
+    def get_travel_diary_service(self):
+        if self.session is not None:
+            return TravelDiaryService(self.session)
+        return None