Better TileSet editor and 256 tiles

• Added Undo/Redo buffer to the tile set editor.
  Press the relevant buttons or CTRL+Z/CTRL+Y to action the undo/redo.
• Added CTRL+Arrow LEFT/RIGHT to quickly switch between tiles in the tile set editor.
  This selects the adjacent tile.
• Added a "Stay in Paste Mode" checkbox.
  When checked and pasting a tile/area in the view editor then the state will not be reset.
  This means that you can select tile/area and use it like a stamp to paste it multiple times.
  The same can we achieved by holding down ALT when pasting; the tile will stay selected.
  Pressing ESC will cancel the paste process and return to the selection mode.
  -The number of tiles has been increased to 256.