assignment 5 finished

12: within RecentCDTVC, try to save place_id, cityName and IndexPath
into NSUserDefaults.
    Met bugs
            1: can not store NSArray into NSArray.
            2: can not create a data structure, need to build another
file as the data structure.
            3: can not store insert non-property value Objective C into
NSUserDefaults.
            4: has Problem with DB, same code .predicate can not run
second time even afte clean up the simulator and DB. The problem only
can be solve with reopen Xcode.
13: fix the DB problem. 'reload the tableView' is important.
    Bugs: 'tableView cellForRowAtIndexPath: cannot access'
    Solution: has to setup 'Table view data source' by setting up 1.
numberOfSectionsInTableView: 2.tableView: numberOfRowsInSection: 3.
tableView cellForRowAtIndexPath: to make sure
numberOfSectionsInTableView is not 0.