Comment 1 for bug 1032945

Depending on the canvas scale, the grid step should be different.

For example, given:
 - px the wished minimum pixels width between two grids subunit,
 - scale the number of pixels to express one world unit (canvas scaling in the range [4 ; 200])

=> grid subunit should be displayed each delta := px/scale

rounding should occur to make it meaningful:
 if delta > 1 then rounding at 0.5 else rounding at 0.05

Need to explore the ideas