Feature Update for Sudoku

Changelog:

• Tried to properly sign the Android .apk
• Tweaks to the colour schemes to hopefully make them a little more readable in general
• Improvements to Light Mode colour choices (sorry)
• Scoring!
• Bug fix: using undo into an old mistake no longer punishes the player
• Bug fix: times should be recorded correctly
• Bug fix: enabling manual checking no longer strips the "correct" colour from squares when you enter a new number
• Bug fix: chill mode now congratulates you when you win!