Prototype 2 - As in "2 players"

A second local player can now join the game!

• Added a lobby where you can add and remove players.
• The amount of monsters is increased by 50% with a second player.
• The circle is slightly bigger with a second player.
• The perks are chosen commonly for both players and will fully apply to both of them.
• The players are invulnerable in the lobby and while choosing their perks. However, they deal full damage to each other during the wave.
• If at least 1 player is alive when the wave is over, the other player will respawn with 0 hp. (It will heal up after choosing a perk, scaling with the Regeneration perk.)