text: Title: Maximize whitespace with feature-reordering optimization in ParallelCoordinates and RadViz
  Body: Both `RadViz` and `ParallelCoordinates` would benefit from increased whitespace/increased transparency that is achieved simply by recording the columns around the circle in `RadViz` and along the horizontal in `ParallelCoordinates`. Potentially some optimization technique would allow us to discover the best feature ordering/subset of features to display. 
  
  ### Proposal/Issue
  
  - [ ] enhance `RadViz`/`ParallelCoordinates` to specify the ordering of the features 
  - [ ] create a function/method to compute the amount of whitespace or alpha transparency in the figure 
  - [ ] implement an optimization method (Hill Climbing, Simulated Annealing, etc.) to maximize the whitespace/alpha transparency using feature orders as individual search points. 
  
  