[Review Only / No Merge] Chess

[ChaseDRedmon]

Implement Chess into OpenPigeon. Tries to attempt feature parity with GamePigeon chess mechanically.

Does not include:

1. settings screens
2. user profile customization
3. music
4. sound effects
5. board preview in iMessage (without going into the game)

Working features:

1. Follows standard chess rules: normal chess moves, en passant, castling
2. Move highlighting for legal moves (blue), capture moves (red), and previous opponent moves (green)
3. Undo move before send with undo arrow
4. Move animation to show chess pieces moving across board for player and opponent

Blocking features:
Waiting for confirmation / research on copyleft or creative commons non commercial licensing on picture assets used in PR

[ChaseDRedmon]

Bug:

Bug with pawn being able to move diagonally without capturing pieces off the starting rank