Add an Autoscroll checkbox to the monitor

Hi

I think it could be handy to add a checkbox to the monitor to enable or disable the autoscrolling of the monitor when new data gets printed. The monitor of the Arduino IDE has such a feature.

The current idea is that if the user is at the bottom of the text, autoscroll is on; if the user scrolls the text, autoscroll turns off. It turns on again when the user reaches the end of the text.

But I noticed it does not work as expected a while ago.