Touchscreen scale should be guessed from calibrate.py

[bwhitman]

A tulip user reached out to say their tulip's CTP was not responding where they thought it should. I built world.download('paint.py') for them to debug and it looks like the scale is off. We allow touch_delta to be set at runtime, but not touch_scale (which is set at 0.8 for the y-axis). We should allow scale to be a runtime var, and also update calibrate to divine a scale.

[bwhitman]

74676676920__5F6EA053-C659-42C4-950C-FACE59579566.MOV

[bwhitman]

We now ship with y_scale being settable by touch_delta. What we don't yet have is a version of calibrate that can guess it. I'll have some users try it out for me.