Editor enhancements

[Bubbler-4]

• Toggle borders between cells (Masterpiets has 1px solid black)
• Show cell count of a selected block
• Resize by entering size
• Reset grid
• Undo/redo edit (for various actions, e.g. grid add/remove row, draw single pixel, import from picture)
• Bulk movement (select a set of pixels and move around or rotate)
• Bulk recolor (select a set of pixels and apply a color offset to all of them, to replace commands in the middle)