Area select tool, move selection up or down px by px

[NicDoesCode]

Currently if you want to move a group of pixels up or down by anything that isn't a whole tile (multiple of 8px) then you need to repaint the part of the image in the new position, which is tedious.

Make it so that you can move an area of the image on a px by px basis.

Things to consider:

• Will any linked tiles be unlinked by the operation?
• Should that be a selectable option?