utils: Display muted messages in all streams except 'All messages'.

We avoid creating MessageBox if the current narrow is 'All messages'.
These messages are however visible in their respective streams.

Tests added.

Fixes #272.

tests/ui/test_utils.py

@@ -109,6 +109,14 @@ def test_is_muted(mocker, msg, narrow, muted_streams, muted_topics, muted):
         [1],
         None,
         True,
+        1,
+    ),
+    (
+        # Don't show in 'All messages'
+        [],
+        [1],
+        None,
+        True,
         0,
     )
 ])

zulipterminal/ui_tools/utils.py

@@ -24,7 +24,8 @@ def create_msg_box_list(model: Any, messages: Union[None, Iterable[Any]]=None,
         # Remove messages of muted topics / streams.
         if is_muted(msg, model):
             muted_msgs += 1
-            continue
+            if model.narrow == []:  # Don't show in 'All messages'.
+                continue
 
         msg_flag = 'unread'  # type: Union[str, None]
         flags = msg.get('flags')