Change used sprites to original ones

[Diapolo10]

Is your feature request related to a problem? Please describe it

The current sprites are basically borrowed assets, and should be replaced by original ones. This includes a car sprite, and the track itself.

Describe the solution you'd like

The project needs new assets for cars and tracks, with the latter split into borders and the track itself.

Describe alternatives you've considered

We could keep using the current assets, but that's not very professional. We want to look professional.

Additional context

The sprite dimensions should ideally be roughly equal to the current ones, and use the same orientation.