Move frequency paramaters to VJ

-Move frequency parameters from stop_time to vehicle_journey, save at least 3* uint32_t per vehicle_journey
-Enforce arrival/departure time in stop_time to be relative from 0
-Calculate low/upper threshold using relative times and VJ frequency paramaters
-Reduces size of stop_time with 8 bytes, increases size of VJ by 16 byes.

IMPORTANT: fails best_stop_time test, but i have a feeling the test is wrong there, please verify.