DuinoCube: Add system reset.
examples: core_usb_demo: remove reset code

It's now done by DC.begin().
examples: use ARRAY_SIZE macro in core_usb_demo

Also rename the arrays with the const naming convention.
examples: Remove unused fields in sprite struct
examples: core_usb_demo: Make game loop counting more clear

- Rename the counter variable to "movement_count"
- The count step is now a #define.
- The loop condition is true rather than left empty.