gitter: Fix occupants for GitterRoom

The limit parameter was not used which defaults to 30
and returns maximum 100 users at a time. Hence, it fails
to return all the members in the room.
In order to tackle this, we need to iterate by skipping
100 members with every API request. Also users count
needs to be updated everytime list of occupants is
requested as new users may join a room in realtime.

Closes errbotio#38

gitter.py

@@ -153,12 +153,13 @@ class GitterRoom(Room):
     def invite(self, *args) -> None:
         pass
 
-    def __init__(self, backend, idd, uri, name):
+    def __init__(self, backend, idd, uri, name, user_count):
         self._backend = backend
         self._name = name
         self._uri = uri
         self._idd = idd
         self._joined = False
+        self._user_count = user_count
 
     def join(self, username=None, password=None):
         log.debug("Joining room %s (%s)" % (self._uri, self._idd))
@@ -185,6 +186,10 @@ def name(self):
     def joined(self):
         return self._joined
 
+    @property
+    def user_count(self):
+        return self._user_count
+
     exists = True  # TODO
 
     def destroy(self):
@@ -205,12 +210,22 @@ def topic(self):
             else:
                 raise RoomNotFoundError("Cannot find the room '{}'".format(self.uri))
 
+    def _update_user_count(self):
+        json_rooms = self._backend.readAPIRequest('rooms')
+        for json_room in json_rooms:
+            if json_room['id'] is self.idd:
+                self._user_count = json_room['userCount']
+
     @property
     def occupants(self):
         occupants = []
-        json_users = self._backend.readAPIRequest('rooms/%s/users' % self._idd)
-        for json_user in json_users:
-            occupants.append(GitterRoomOccupant.build_from_json(self, json_user))
+        self._update_user_count()
+        for skip in range(0, self.user_count, 100):
+            # 100 is the maximum number of users Gitter API can return.
+            json_users = self._backend.readAPIRequest(
+                    'rooms/%s/users?skip={}?limit={}'.format(self.idd, skip, 100))
+            for json_user in json_users:
+                occupants.append(GitterRoomOccupant.build_from_json(self, json_user))
         return occupants
 
     def __eq_(self, other):
@@ -369,7 +384,7 @@ def rooms(self):
             if not json_room['oneToOne']:
                 log.debug("found room %s (%s)" % (json_room['name'], json_room['uri']))
                 rooms.append(GitterRoom(self, json_room['id'], json_room['uri'],
-                                        json_room['name']))
+                                        json_room['name'], json_room['userCount']))
         return rooms
 
     def contacts(self):