Add API to get recent messages.
Modify API package hierarchy
Add options for message list API
Implement permission check to get messages list
Add specs for Message model

- Fix FactoryBoy usage
Improve specs codes

- Get rid ob obj.save()
- Factory returns a model that sequential unique fields.
Add Spec for message list API.
Add RoomManager specs
Set default value for Room#description
Move a logic that add member when user accessed to a room.
Hide author field on RoomCreateView and add specs closes #1601