Speed up charge geometry loading

[mjkramer]

This is mainly for ND-LAr. It was taking ten minutes to initialize the pixel coordinates LUT. Now it takes about a minute.

• Generate the LUT's keys just once, instead of 35 times
• Add a LUT.set_scalar method optimized for setting one element at a time
• Avoid a bunch of function calls that just repeatedly calculate "IO groups per module"
• Add a progress bar since it's still kinda slow