add topic model class
topic list vc: replace topic string by model
command vc: replace topic name by command name
topic vc: replace useless properties by topic model property
topic list vc: assign topic model to cell view
topic list vc: replace segue by button action
topic list vc: implement present view controller for topic
topic list vc: alloc topic object for redis for the moment
topic list vc: implement choose topic action
topic list vc: update constraints to cell