adds log update function and log list

- log updates in background automatically
  from server data
- log list in main screen of app is updated
  showing the title of each notification

app/src/main/res/values/strings.xml

@@ -13,6 +13,8 @@
     <string name="scan_sender">Scan</string>
     <string name="camera_fragment_label">Scan Sender QR</string>
     <string name="preference_file_key">code_file_key</string>
+    <string name="message_header">messages received:</string>
+    <string name="default_nr_messages">0</string>
     <string name="code_key">code_key</string>
     <string name="notification_title">Bump</string>
     <string name="bump_notification_channel_id">bump_id</string>