BUG #0013810. Fixing PointSprites panel to work with new panels.

This is a quick hack, simply duplicating the existing code from
pqPointSpriteDisplayPanelDecorator in pqPointSpriteControls. There is
considerable cleanup that is needed to ensure this representation works in a
coherant manner with the rest of the application (currently this representation
uses several non-standard *tricks* that can easily break.

Change-Id: I3b6748b8f60d77890f1fa690a32150ca100b3eb7
Merge topic 'refactor_panels' into next

7017d50 BUG #0013810. Fixing PointSprites panel to work with new panels.