Improve movement in examples

[Jondolf]

Objective

Fixes #170.

Currently, the movement in examples like move_marbles and cubes is frame rate dependent because they are running in Update but don't use delta time. basic_dynamic_character and basic_kinematic_character on the other hand run in the PhysicsSchedule, but this can cause issues with missed inputs as reported in #170.

The character controllers are also perhaps too basic and don't reflect real usage well, and the movement code isn't great and it doesn't support WASD.

Solution

• Put all movement systems in Update and use delta time (alternatively, you could send input events in Update and have another system handle the movement in the PhysicsSchedule)
• Refactor input handling to be cleaner and to support WASD as well as arrow keys
• Refactor character controller examples with CharacterControllerBundle and configuration options
• Fix some meshes not being rendered due to clone_weak