Particle mutate up to event (not timestamp)

[tmelliott]

In the case that Event is a GPS position

• travel until delta = 0

In the case that Event is a stop time update

• travel at least until delta = 0
• continue travel ahead until particle arrives at (and departs, if departure Event) e.stop_index

When commencing an iteration

• remove delta_ahead from delta to wait for vehicle to catch up to particle
• if departure_time > _timestamp, randomise remaining dwell time (allows resampled particles to diversify)

Other

• if at a stop, be sure to set departure_time when leaving stop