Paper_column::print can be very helpful in debugging spacing
information, but until now its output was not very readable.
This patch:
- decreases font-size of debugging info so that it doesn't
collide and overlap everywhere,
- makes it possible to override the size of the arrow values
with font-size property,
- makes both red and blue arrows point in the same direction
(previous situation was confusing)
- centers the spring and rod values on the arrows (previously
it was hard to discern which number goes to which arrow),
- prints debugging info always on top,
- makes arrows and the distance between them scale with fontsize.