Use tsconfig inheritance

[sverhoeven]

Typescript 2.1 will have Configuration Inheritance

This will make the generated tsconfig.json much simpler like

{
 "extends": "node_modules/@nlesc/react-scripts/config/tsconfig.json"
}

In the @nlesc/react-scripts package the base tsconfig (config/tsconfig.json) will be stored.

Nice if instead of full file path, a path inside a package (@nlesc/react-scripts/config/tsconfig.json) could be used.

This will make the @nlesc/react-scripts have less generated configuration, but still be overwrite-able.