get globalConfig() {
        if (!this._globalConfig) {
            fs.ensureDirSync(this.constructor.globalDir);
            this._globalConfig = new Config(path.join(this.constructor.globalDir, 'config'));
        }

        return this._globalConfig;
    }
Global config (lives at ~/.ghost/config). This config is primarily
responsible for storing all of the Ghost instances on a particular system.

@property globalConfig
@type Config
@public