[GSOC] Tiled Rendering, ahunt, Weekly Report 12 / WK32

Hi All,

This week was primarily work on the Calc Tiled Rendering:

* Realised on Friday that my current approach was probably a huge waste
  of time.
** Using logic mapping makes cell sizes etc. correct, but breaks
   lots of assumptions meaning that the usual Calc UI is quite broken
   (problems/corruption with repainting when scrolling etc.)
** Requires lots of debugging/digging to adjust those parts (the code
   is quite complex...).
** Instead we can keep pixel mapping, but use the
   LogicToPixel/PixelToLogic( Object, MapMode) methods to do our own
   conversion directly before painting in the appropriate places
   (allowing use of pixel-based adjustments as needed), and meaning
   that most code (around scrolling/repainting) can stay with pixel
   coordinates as before.

* But fortunately a large portion of the commits are vaguely reusable
  (with some adjustment) for the new approach, i.e. they indicate most
  of the relevant places in the code that still need adjusting.
** Started this work on a new branch:
   feature/calctiledrendering_simpler.

Cheers,
        Andrzej