Add shuttling-aware adjusted counts to TripCounts

[idreyn]

This ticket proposes two new fields on the TripCounts table:

• adjustedCount
• adjustedByHour

These adjusted values count "partial trips" that only run part of their route's usual length due to shuttling. For instance, if an RL-B trip is shuttling north of Harvard, then we'd only count that as 15/18 ≈ 0.833 trips (excluding the northernmost three stations). This means the reduction in service quality from shuttling will be reflected in this metric, and the trip counts will remain robust to shuttling edge cases (like where the line is split into two functional segments by downtown shuttling).

In the lastest GTFS feeds we can use trips from the fake CalendarService called canonical to determine how many stops an un-shuttled RoutePattern should have. In the historical feeds, I think we can use RoutePattern.representative_trip_id.