Add support for react native

[macrozone]

It would be cool to be able to generate react-native apps in the future.

maybe mantra create-native myapp ?

A good sample project is https://github.com/inProgress-team/react-native-mantra-boilerplate

We need new templates for this. To make this task easier, we probably should refactor the code-generators more, so that it's easier to reason about which files should be created when generating a project or entity