Tweak how we interpret failed retrievals (timeout, car_too_large)

[bajtos]

• car_too_large should not be counted as a failure or a success. Also, add a new chart to visualise % of car_too_large measurements
• timeout - let’s distinguish between “cannot reach the server at all” and “timed out while downloading data”. First is a failure, the second should be treated similarly to “car_too_large” (including another visualisation).