This PR addresses some issues around the "size" scaling that was
not very usable beside the basic usage. Several changes:
* Scaling is *area based* (which is the perceptually right thing)
* Removed the "reverse" button and switch that was actually meaningless
  in many cases
* Differentiate between linear and flipped-linear mapping (that span the
  whole min-max range) and "absolute" mappings including proportional,
  log, sqrt, inverse that instead use an "absolute" scale

NB this is another breaking change as it removes the "reverse"
option that was frankly useless

This PR addresses some issues around the "size" scaling that was
not very usable beside the basic usage. Several changes:
* Scaling is *area based* (which is the perceptually right thing)
* Removed the "reverse" button and switch that was actually meaningless
  in many cases
* Differentiate between linear and flipped-linear mapping (that span the
  whole min-max range) and "absolute" mappings including proportional,
  log, sqrt, inverse that instead use an "absolute" scale

NB this is another breaking change as it removes the "reverse"
option that was frankly useless

…ize-cleanup