messages: Show headers if is_search_narrow().

Previously, when text searching, messages appear
adjacently under the same heading, this can be confusing since they
appear sequentially but there may be messages inbetween that don't meet
the search criteria. Fixes part of zulip#1550.

zulipterminal/ui_tools/messages.py

@@ -123,6 +123,14 @@ def need_recipient_header(self) -> bool:
         if self.model.is_search_narrow():
             return True
 
+        if self.model.is_search_narrow():
+            if len(self.model.narrow) == 1:
+                return True
+            if len(self.model.narrow) == 2:
+                return not self.message["type"] == "private"
+            if len(self.model.narrow) == 3:
+                return not self.model.narrow[1][0] == "topic"
+
         last_msg = self.last_message
         if self.message["type"] == "stream":
             return not (