Update post jam

Post game jam update to have a full game, adding  :

Gameplay :

• General rebalancing
• More easy at start, difficulties appear more gradually
• Only five full levels
• Add bonus ovni flying saucer
• Countdown score to previous level when retrying a level

UI :

• Add retry screen
• Add skipable countdown for screens
• Add 5 best hiscores table

Effects :

• Add flash and implosion when dying
• Add bonus points
• Victory ending effects

Sounds :

• New ambiance, progressive rythme speed
• Flying saucer alarm
• Music for victory ending

Enjoy !