More refactoring

it's going to be great...
@ryancoughlin This is one part of the code that makes the view scale dynamically. The drawing code in `drawRect:` will happily redraw the scale at the right size. But the markers aren't part of that code. They're subviews, whose position is determined by the value they want to represent. By resetting their values in `layoutSubviews`, their correct y-position gets recalculated and they move to the right position.