views: Append topic links in message info view.

The topic and message links is generalised with a member function.
It sets the desired dimensions and widgets (now member variables)
and handles topic links if present.

Tests amended.
Fixes #709.

zulipterminal/ui_tools/views.py

@@ -1145,6 +1145,8 @@ def __init__(self, controller: Any, msg: Message, title: str,
                 ('Edit History', 'Press {} to view'.format(keys))
             )
         # Render the category using the existing table methods if links exist.
+        if topic_links:
+            msg_info.append(('Topic Links', []))
         if message_links:
             msg_info.append(('Message Links', []))
         if time_mentions:
@@ -1167,32 +1169,39 @@ def __init__(self, controller: Any, msg: Message, title: str,
         self.widgets = (self.make_table_with_categories(
                         msg_info, column_widths))
 
+        # slice_index = Number of labels before links + 1 newline
+        #               + 1 'Links' category label.
+        self.slice_index = len(msg_info[0][1]) + 2
+        if topic_links:
+            self.set_links(topic_links)
         if message_links:
-            message_link_widgets = []
-            message_link_width = 0
-            for index, link in enumerate(message_links):
-                text, link_index, _ = message_links[link]
-                caption = '{}: {}\n{}'.format(link_index, text, link)
-                message_link_width = max(
-                    message_link_width,
-                    len(max(caption.split('\n'), key=len))
-                )
-
-                display_attr = None if index % 2 else 'popup_contrast'
-                message_link_widgets.append(
-                    MessageLinkButton(controller, caption, link, display_attr)
-                )
-
-            # slice_index = Number of labels before message links + 1 newline
-            #               + 1 'Message Links' category label.
-            slice_index = len(msg_info[0][1]) + 2
-            self.widgets = (self.widgets[:slice_index] + message_link_widgets
-                            + self.widgets[slice_index:])
-            self.popup_width = max(self.popup_width, message_link_width)
+            if topic_links:
+                self.slice_index += (len(topic_links) + 2)
+            self.set_links(message_links)
 
         super().__init__(self.controller, self.widgets, 'MSG_INFO',
                          self.popup_width, title)
 
+    def set_links(self,
+                  links: 'OrderedDict[str, Tuple[str, int, bool]]') -> None:
+        link_widgets = []
+        link_width = 0
+        for index, link in enumerate(links):
+            text, link_index, _ = links[link]
+            caption = '{}: {}\n{}'.format(link_index, text, link)
+            link_width = max(
+                link_width,
+                len(max(caption.split('\n'), key=len))
+            )
+
+            display_attr = None if index % 2 else 'popup_contrast'
+            link_widgets.append(
+                MessageLinkButton(self.controller, caption, link, display_attr)
+            )
+        self.widgets = (self.widgets[:self.slice_index] + link_widgets
+                        + self.widgets[self.slice_index:])
+        self.popup_width = max(self.popup_width, link_width)
+
     def keypress(self, size: urwid_Size, key: str) -> str:
         if (is_command_key('EDIT_HISTORY', key)
                 and self.show_edit_history_label):