Refactors to prepare for score tracking+high scores leaderboard

[varoonp123]

Some preliminary work as I started working to some score counting with the following rules. Commits are quite atomic.

Scoring ideas

You get points for the following actions:

• Firing a shot that hits/damages an enemy Mob (points=damage dealt)
• Destroying an enemy Mob (fixed amount for each mob)

You lose points for:

• Damaging your ally (points=damage dealt to ally mob)

[cdsupina]

You could also lose points for letting enemies get past you.