Post jam bug fixes and balancing

Bug fixes:

1. Fixed a bug where mobs would get stuck at the start
2. Fixed a bug where mobs would move the wrong direction off the screen
3. Fixed a bug where you were getting the incorrect amount of bonus gold at the end of a wave
4. Fixed a bug where Empowered Chilling Vine was not freezing

Balance changes

1. Added the chilling effect to splash damage
2. Empowered Chilling Vine now chills in a splash radius
3. Removed floating damage numbers because it was cluttering up the screen too much
4. Adjusted the cost and stats of all towers