Fix, improve, and refactor distortMaxValuesBy

- The calculation used to determine how much to scale graph values to
  additionally fit flags, labeling, etc. was incorrect and is now
  fixed. Previously if the total graph area was 100 and labeling took
  up 20 pixels a scale factor of 1.2 was returned.  The desired effect
  in this case is to have the bars take up 80 pixels, so the scale
  factor should have been 1.25.
- When determining the amount of pixels needed for labeling, the text
  from the longest label is used.  When injected to discern the height
  from the DOM element, it is injected as HTML so character codes are
  reduced to a single character.
- Refactored distortMaxValues to improve readablity and to make it
  more consistent with the rest of the code in Elroi.