followed online tutorial
#Concentration This app is the concentration game from Stanford opencourse lecture
url:https://www.youtube.com/watch?v=71pyOB4TPRE&list=PLPA-ayBrweUzGFmkT_W65z64MoGnKRZMq
#Autolayout_progmatically Project from online tutorial
- set up autolayout without using storyboard
- using collectionView to present three pages
- use stack container to contain the bottom bottons and page controller
- follow MVC
url: https://www.youtube.com/watch?v=9RydRg0ZKaI&list=PL0dzCUj1L5JHdeOlzJtp5zlsdrliJTC7F