Refac xs

Refactored the 2-D cross section viewer to allow:
- the image size to be changed
- to fix a blitting issue
   - If you clicked on the image to freeze the horizontal and vertical cuts then changed the image then clicked again to un-freeze the horiz and vert cuts, then the old blit would appear until you moved the cursor off of the canvas which would trigger a re-draw and the new image would appear again