Enphaderz Upgrades Implementations

Yet another partial implementation, but nonetheless, it IS progress.
Added support for the Derp Modifier (Making it feasible to invest your
time in this game)
Implemented a Health bar, affected by the health upgrade.
fixed a glitch where if the player left in the middle of a wave, where
it wouldn't count the current wave's derps.
fixed the equation for calculating the derp modifier.