gerberToPNG() method incorrectly processes gerbers

[stansanders]

currently gerberToPNG sets the PNG output dimensions to the outermost data in the gerber, however this causes an incorrect output for normal copper layers that don't have a dimension or ground pour. The incorrect output is such that the PNG is the dimensions of the traces rather than the board, and the traces keep their offset from the board edge which causes traces to be cropped off.

If we rework the image_to_laser moves script to accept the profile gerbers in addition to the copper layer, gerberToPNG could use the profile to set the dimensions correctly.