additional script

I wanted to see how easy it would be to lock two scales to the same
position. This can be used for proportional scaling of width /height,
especially for very fine resolution scales.
additional feature to grid

Added the ability to lock the value of both sliders to one single value,
to provide a square grid. code from commit
ad19c2d4d3aec29601b77488ec83b928bec3e1b9