Step 1: Add a new ViewController as rootVC

- Add view controllers (Timer, History) to project
- Set each viewcontroller's tabBarItem.title and tabBarItem.image
- Initialize a tab bar controller
- Initialize each view controllers
- Set viewControllers as tab bar controller viewControllers
- Set tab bar controller as root viewcontroller of window

Signed-off-by: Taylor Mott <trm36@humboldt.edu>