[SpeedGrader] Allow students to annotate using touchscreens (Chromebook)

I love the new student annotation feature, however the students are only able to annotate using the keyboard and mouse/touchpad. We would love for students to be able to use their finger to draw on the screen for annotations. For use cases like making quick sketches or graphs. Right now, using your finger will just make the page scroll up and down instead of allowing for use of the annotation tools.