Major Update

Changes:
- Added new weapon that only spawns once per level
- Changed max number of weapons from 8 to 4. Because of that the ships have been redesigned
- When playing on "God Hard" difficulty your weapons have limited ammo. Ammo refills when activating your Special Ability
- Many enemy behavior improvements.
- Improved Tutorial
- Made playing the Tutorial once mandatory (because everyone was ignoring it)
- Improved HUD (a little)
- Corrected score calculations
- Many redesigned sprites (goodbye programmer art)