Added missing stages + fixed small score bug

Finally added the missing backgrounds for the bosses which still didn't have one! Now, each boss has its own stage:

• Kachukko: Back Alley
• Bramba: Pier
• Zawas: Helipad
• Vesper: Cemetery
• Planz: Arboretum
• Becue: Power Plant
• Dragato: Bridge
• Crawbo: Beach
• ???: Impact Crater

Here's some of them!

Also, I've fixed a bug that didn't allow the score to be displayed correctly in arcade mode on game over before reaching the final boss.