Disabled the tile data pooler.

Now nothing should prevent the swapper to do it's work. And big images
should work ok.
There are two bugs still:
1) When you load a big jpeg image, it is loaded entirely to your
memory. And right after that the swapper comes and swaps it out of
your memory.
2) resizeEvent() for the canvas creates a QImage as big as your image
and then deletes it.