Add support for project-specific rn-cli.config.js

Whackage now supports project-specific packager configurations. In order to use this feature, your configuration must conform to the following spec.

1. Your config file needs to be called rn-cli.config.js, and be present in the project root directory
2. Your getBlackListRE method must take an optional array of "default" modules to blacklist, and pass those to blacklist along with your own blacklisted modules.

Example:

// rn-cli.config.js
const blacklist = require('react-native/packager/blacklist');

module.exports = {
  getBlacklistRE(defaults = []) {
    const modulesToBlacklist = [
      /* ... your deps */
    ];

    return blacklist(defaults.concat(modulesToBlacklist));
  }
};

Any other configuration methods should work out of the box without modification.