CLI: Add support for project templates

[mkonicek]

Currently it is not trivial for people to get started with React Native. react-native init MyApp just creates a simple app with a single screen. People have to spend time figuring out how to add more screens, or how to accomplish very basic tasks such as rendering a list of data or handling text input.

Let's add an option: react-native init --template navigation - this creates a "starter" app which can be easily tweaked into the actual app the person wants to build.

Test plan (required)

• Checked that 'react-native init MyApp' still works as before:

• Ran 'react-native init MyNavApp --template'. This prints the available templates:

$ react-native init MyNavApp --template
...
The available templates are:
navigation
You can use these to create an app based on a template, for example: you could run: react-native init MyNavApp --template navigation

• Checked the template works:

$ react-native init MyApp --template navigation
...
$ cd MyApp
$ react-native run-ios

• Checked an error is printed when a bad template name is provided:

$ react-native init MyNavApp --template foo
Setting up new React Native app in /private/tmp/MyNavApp
readline.js:982
            throw err;
            ^

Error: Uknown template: foo

[ericvicenti]

The template generator code is looking great!

Only feedback is that I think a TODO app may be a preferable example. Also it may be nice to have a stack in the example, because stack navigators are super common.

[mkonicek]

Thanks for the review! While building the Chat example I realized it shows most of the concepts well, and a Todo app might be a bit boring? Not a strong opinion though..

The app is using a StackNavigator - it's the top level one, and the TabNavigator is nested inside it. (This PR doesn't contain the whole app but just tweaks it. The app template was committed before and lives here: https://github.com/facebook/react-native/blob/master/local-cli/templates/HelloNavigation).

[mkonicek]

I'll merge it for now and iterate on the template.

@facebook-github-bot shipit-ninja

[mkonicek]

@facebook-github-bot shipit-ninja

[facebook-github-bot]

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[facebook-github-bot]

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