Refactor code to split between GridData and StintData

[vekkiokonio]

Need to refactor RaceData struct.

First, add a stint: StintData field to GridData to avoid repeating field (and to ensure consistency).

Second, verify if there is a better way of refactoring RaceData. For instance, evaluate if it makes sense to have three field (data, stint, history) instead of merging data and stint as it is now.