The JSplitPane has an API to set the location of the divider in terms of pixels.
This is fine, but whenever the panes size changes that divider location may not
provide the appearence that the developer intended.

Provide an API to specify proportional divider location where by

0.0 means the minimum location (0 pixel) and 1.0 means maximum location (i.e.
width of the JSplitPane).