Let vehicles wait before driving to prebooked pickup

[sebhoerl]

Currently, the task chains of the vehicles are constructed as

[current task] [drive] [wait] [pickup]

for prebooked requests, i.e. the vehicle will wait until the earliestStartTime of the requests before starting the pickup task. However, it may actually be more intelligent to wait at the initial position and arrive right before the pickup. This means, the scheduler should be modified such that it can create chains like

[current task] [wait] [drive] [pickup]