add background manipulating inputs
Adjust background image dimensions via html input
dry up bg dimension setting listeners
Hide bg image controls until bg image set
move grid controls to bottom
add inputs for grid dimensions
move midpoint calculations into column/ row functins
rebuild grid on user dimension change
use global variable for label offset
reset midpoint arrays after changing dimensions
prepopulate grid dimensions inputs
store gridpoints in each code box
add checks to confirm gridpoints exist on existing boxes
reposition grid boxes on grid dimension change
reposition codeboxes on grid dimension change
delete boxes that no longer fit on the grid