Increase / Decrease Code Font Size (last tasks)

This should complete the tasks in this [Trello Card](https://trello.com/card/2-increase-decrease-code-font-size/4f90a6d98f77505d7940ce88/462).

Unfortunately chrome doesn't trigger a mouse wheel event when control is pressed, so I had to use Shift + Mouse Wheel Scroll.

The scroll restore isn't still right, but the problem should fixed once #3115 is fixed.