model/views: Add method to regularly update state markers in messages.

This commit:
 * introduces a method `update_msg_list_presence_markers` in middle column
   view class. It would be responsible for rendering the status markers
   (if present) in message list.
 * adds presence renderer function to the handler `start_presence_updates`.
   This way, the method `update_msg_list_presence_markers` is called every
   minute.

The helper `update_msg_list_presence_markers` uses MessageBox class method
`update_msg_content_header` (added in previous commit) to update a message
box (if required).

Fixes zulip#896.

Author: Ezio-Sarthak

zulipterminal/model.py

@@ -354,6 +354,8 @@ def _start_presence_updates(self) -> None:
                 if hasattr(self.controller, 'view'):
                     self.controller.view.users_view.update_user_list(
                         user_list=self.users)
+                    (self.controller.view.middle_column
+                        .update_msg_list_presence_markers())
             time.sleep(60)
 
     @asynch

zulipterminal/ui_tools/views.py

@@ -525,6 +525,18 @@ def get_next_unread_pm(self) -> Optional[int]:
             return pm
         return None
 
+    def update_msg_list_presence_markers(self) -> None:
+        for index in range(len(self.body.log)):
+            msg_btn = self.body.log[index]
+
+            # Update a message box content header if required.
+            msg_btn.original_widget.update_msg_content_header()
+
+            # Render the modified message list
+            self.body.log[index] = msg_btn
+
+        self.controller.update_screen()
+
     def keypress(self, size: urwid_Size, key: str) -> Optional[str]:
         if is_command_key('GO_BACK', key):
             self.header.keypress(size, 'esc')