The blur was created because the original svg ruler was too small. This
patch increas the base size of the image by a factor of 10, and reduce
the displayed size accordingly.

This event is also recognized by Firefox

This patch should produce the same result on Chrome but fix the display
on Firefox.

This commit change the design of the ruler and place all the elements in
a svg g element. This allows to use transforms instead of calculating
all the x,y coordinates of all staring and ending points of every line