Removed unnecessary HTHEME parameter in getFrameControlCheckboxSize().
Added code for distinguishing column types to drawCell().
Started writing the checkbox drawing code. Just a red box again for now.
Wrote up toItemContentRect() and used that in drawCell(). More TODOs.
toItemContentRect() -> toCellContentRect() (consistency)
Made toCheckboxRect() take the xoff parameter too.
Added mouse tracking code. Not used yet.