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

@@ -205,12 +205,22 @@ def topic(self):
             else:
                 raise RoomNotFoundError("Cannot find the room '{}'".format(self.uri))
 
+    def _user_count(self):
+        json_rooms = self._backend.readAPIRequest('rooms')
+        for json_room in json_rooms:
+            if json_room['id'] is self.idd:
+                return 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))
+        user_count = self._user_count()
+        for skip in range(0, 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):