feat(drt|accessibility): DRT Level of Service Output + Integration into DRT Accessibility

[jakobrehmann]

This PR allows spatially and temporally heterogenous DRT level-of-service (LOS) to be estimated in the last iteration of a MATSim simulation. For each combination of origin, destination, and departure time, the DRT dispatcher is queried for a suitable DRT trip, based current simulation state. However, these hypothetical trips are never fulfilled, and thus do not affect the DRT's sensitive balance between supply and demand. As a standalone module, this contribution can provide useful operational information about DRT, especially in areas and time periods where there are few or no simulated DRT trips. However, it can also be used in combination with the DRT accessibility framework (#3626), to allow spatially and temporally heterogenous DRT accessibility calculations based on a simulated DRT service.

The LOS can be calculated either:

1. ZONE-TO-ZONE: A grid with a user-specified granularity is superimposed over the DRT service area; cells not containing DRT stops are filtered out. DRT service quality is probed for each combination of zones.
2. STOP-TO-STOP: service quality is probed between each combination of DRT stops. User may specify which stop combinations are relevant for the accessibility calculation to reduce computation cost.