Enhance collision check algorithm

[Cyril Stoller]

Bug reported: Bullets goes still through deflectors on some users.

• Fix: (work around): reduce bullet speed -> collision check routine is called more often.
• Implement Bullet animation as separate scheduler (with more fps than the default animation scheduler)
• Implement collision check like in the Kivy game Cocaine

[Cyril Stoller]

Fix done in v1.0.1: reduced max bullet speed to 75%.