Tasks to complete for v0.2.6

[boaromayo]

For v0.2.5 tasks:

• Add and fix undo/redo functionality
• Prompt user when changing tilesets

For v0.2.6 tasks:

• Add cut, copy, paste functionality
• Make error prompt if user places invalid input on spinners in dialog boxes
• Enable saving maps in .csv and .json formats
• Move lock button to grid sizes panel