Rework of iterators

[Casper Boemann]

> > Krita is at an important crossroads - lets please go the right way - as
we
> > have already decided.
>
> I might not have fully understand, what do you call a pixel iterrator ? At
> line 49 of kis_pixel_iterator.h you return a Q_INT8 which is a QUANTUM !
> In mymind, a pixel iterrator is something that return a structure
representing
> a pixel like in KisPixelRepresentation (on which we have agreed).

yes a pixel iterator returns a structure representing a pixel.

You should not take my Q_INT8 * as meaning a QUANTUM. It should be taken as
a generic pointer to a KisPixel. However Boudewijn didn't wan't to take that
final step of actually returning a KisPixel *.

Note I say KisPixel and not KisPixelRepresentation. This just to emphasize
that I find the KisPixelRepresentation problematic because it assumes that
all channels are of the same type. This can always be refactured later
though so this is something we don't need to argue over now.

I think we are on to something here. I think that we should discuss the
pixelrepresentation and how it relates to channels, channelinfo and the
datatype of channel.

If we aggree on this (even though we may not implement it straight away)
then we would be able so understand better the iterators.

best regards
Casper Boemann