Implement Spritesheet editor functionality

[lbussell]

Todos for Spritesheets

• [ ] Spritesheet
  • [ ] Editing
  • [x] Pencil
  • [ ] Bucket (super broken)
  • [x] Add sprite
  • [x] Remove sprite
  • [x] Display
  • [x] Data
  • [x] Tile Grid
  • [x] Pixel Grid
  • [x] Export header
  • [ ] Export source
  • [x] Export image (should be easy, not tested though tested, works)
  • [ ] undo
  • [ ] redo
  • [x] local storage
  • [ ] Import
  • [ ] drag and drop ?
  • [ ] autotile
    • import, then crop to 256x256, then quantize each tile???
• [ ] Sprite
  • [x] Editing
  • [x] Display
• [ ] Sprite panel
  • [ ] New sprite form
  • [x] implement form
  • [ ] style form
  • [x] button for removing sprite
  • [x] input for changing palette row
  • [ ] style list
  • [ ] allow list to scroll when it overflows the bottom of the screen

[JohnBeckner]

Sprites now have a getter that returns it's list of tiles, useful for exporting spritesheets. Tile reduction should be a stretch goal.