user status: Add "status_text" support in the backend.

You can now pass in an info field with a value
like "out to lunch" to the /users/me/status,
and the server will include that in its outbound
events.

The semantics here are that both "away" and
"status_text" have to have defined values in order
to cause changes.  You can omit the keys or
pass in None when values don't change.

The way you clear info is to pass the empty
string.

We also change page_params to have a dictionary
called "user_status" instead of a set of user
ids.  This requires a few small changes on the
frontend.  (We will add "status_text" support in
subsequent commits; the changes here just keep
the "away" feature working correctly.)

zerver/lib/user_status.py

@@ -1,22 +1,44 @@
+from django.db.models import Q
 from django.utils.timezone import now as timezone_now
 
 from zerver.models import (
     UserStatus,
 )
 
-from typing import Set
+from typing import Any, Dict, Optional
 
-def get_away_user_ids(realm_id: int) -> Set[int]:
-    user_ids = UserStatus.objects.filter(
-        status=UserStatus.AWAY,
+def get_user_info_dict(realm_id: int) -> Dict[int, Dict[str, Any]]:
+    rows = UserStatus.objects.filter(
         user_profile__realm_id=realm_id,
         user_profile__is_active=True,
-    ).values_list('user_profile_id', flat=True)
+    ).exclude(
+        Q(status=UserStatus.NORMAL) &
+        Q(status_text='')
+    ).values(
+        'user_profile_id',
+        'status',
+        'status_text',
+    )
 
-    return set(user_ids)
+    user_dict = dict()  # type: Dict[int, Dict[str, Any]]
+    for row in rows:
+        away = row['status'] == UserStatus.AWAY
+        status_text = row['status_text']
+        user_id = row['user_profile_id']
+
+        dct = dict()
+        if away:
+            dct['away'] = away
+        if status_text:
+            dct['status_text'] = status_text
+
+        user_dict[user_id] = dct
+
+    return user_dict
 
 def update_user_status(user_profile_id: int,
-                       status: int,
+                       status: Optional[int],
+                       status_text: Optional[str],
                        client_id: int) -> None:
 
     timestamp = timezone_now()
@@ -26,7 +48,11 @@ def update_user_status(user_profile_id: int,
         timestamp=timestamp,
     )
 
-    defaults['status'] = status
+    if status is not None:
+        defaults['status'] = status
+
+    if status_text is not None:
+        defaults['status_text'] = status_text
 
     UserStatus.objects.update_or_create(
         user_profile_id=user_profile_id,