Summary:
Create the initial Core Components tutorial. The core components are `Text`, `Image`, `View`, `TextInput`, `ListView`.
1. Provide a summary for each core component, including a runnable sample.
2. Allow the tutorials for each component to be extended with more details and detailed examples, particularly after we add other tutorials (i.e., around state and props).
3. The samples should be runnable in a React Native simulator, if we can get that going in the docs.
4. Reorganize the docs sidebar to make the current Tutorial actually a Sample App, etc.
Closes https://github.com/facebook/react-native/pull/7593
Differential Revision: D3313563
Pulled By: JoelMarcey
fbshipit-source-id: cfe1d397d60822b8c531405d66b4e73694c7dbf9
Joel Marcey