Update To bevy 0.6.0

[wendivoid]

This could be made simpler by first removing the bevy_sky crate as well as the bullet tracer effects. Those are currently the only two parts that use the old renderer and since the both in piss poor condition it's probably better to just remove both of those.

Known Problems:

• Remove bevy_sky crate
• Remove Bullet Tracer Plugin
• remove '.system()' from system insertion locations
• Rename PointLight to Light
• Change AppBuilder usage to App