Rename VecXX::set(index, value) to setComponent

 - Prevent me (and probably others too) from doing the stupid
   mistake of calling vec.set(0,0) and expecting it to have
   x=0 and y=0 while instead just setting x=0.
 - Add new methods
Scrolling enhancements.

 - Allow absoulte/relative changes of content inside
   ScrollingDecorator and ScrollBars.