Database implementation for BattleShip

[mattcasey02]

Implemented the database for Battleship.

• When a user joins a Battleship game, a default document is made in firebase for them (tied to their username) if they do not already have a document in the database
• Upon the game ending, both players data is pulled from the database
• The wins/losses entries are incremented accordingly
• The history entry gets prepended with an object that specifies the opponent's name and whether this player won
• The ELO is updated using standard formulas for ELO, can be found on Wikipedia

Default ELO rank is 1000 and K-factor is 32

[mattcasey02]

Nice work! Do you think we can round each player's ELO to the nearest whole number or floor it so we don't have trailing values?

Note: I am basing this question on the display shown in the cheat sheet PR, so if it's obsolte, there's no need to change anything.

I think it is better not to round, as this maintains a higher accuracy of the ELO system. We can call Math.round on the frontend to make the display an integer.