Add control for dot/Marker ratio

[brettfiedler]

From Slack:

JG
Now that it is working, I am finding it might be a little TOO sensitive and paper points are often detected as markers. If anyone finds that annoying, let us know and we can maybe make the size difference between points and markers something you can control manually during calibration.

BF
I think this will probably depend on the absolute size of the paper dots. Easier to trigger with smaller dots. Keeping papers in the same plane will be important... Need to keep that in mind and decide if there is something to change later. I think it's all good for now. I'll add a note to possibly add separate marker calibration or a control for the ratio later.

If markers are frequently mistakenly recognized during our experiments, we'll add a control (slider or a few predetermined selectors) to control the ratio of dot size where it turns over to a marker. Right now it is set to 3x the dot size determined at calibration.