Various Paint fixes and improvements
- Bug 554: Tile in all modes even if no matching tile is not in the Wimp pool (ref bug 554)
- Fix for 2nd use of insert/delete rows/columns not completing on click
- Use flags in place of hex constants
- Insert default palette when translucent merging into <= 256 colours (counterpart for bug 604)
- Fix for ignoring Ctrl-Scroll & Shift-Scroll on sprite windows