fixup help: if two lines of unit traits, don't use three lines

This commit adds the code which figures out how to add proper
spacing to preserve the desired alignment, accounting for not
using a fixed width font.
fixup traits in help: when two lines used, align the : characters

This fixes up the previous commit, so that even if the numbers of
traits to be assigned from each group are different, the :'s will
end up aligned, by measuring the font-width of the entire rendered
first line label, and subtracting the amount due to the number to
appear in the second part, and assigning this much whitespace.