adds batched output for logging

Recently I have been reading a lot the `bin` code and noticed [these lines](https://github.com/gulpjs/gulp/blob/master/bin/gulp.js#L181-L183). 

- adds `lib/batchThese.js`
- modifies logging for `task_start` and `task_stop` events so the output is batched. 

The reason for adding a batched output for `task_stop` is because sometimes the non-batched output for `task_stop` would write to `stdout` before the batch of `task_start`. I have took a constant length of 4 for the batch instead of 5 because on my 24'' monitor, when I have the terminal window at half the line breaks sometimes.