Procedurally Generated Wave Tuning

The procedurally generated levels start out a little easy, but were getting impossible pretty quickly. Adjusted the enemy spawn math to be a little less aggressive. Also added a health pickup with each spawn group ( in the PG waves) when the player has less than 4 health. This seems generous. But I need it to get very far at all!

Also slowed down the skitters (the purple enemies) a little.