Record duration for pre-generated charge station connectivity data

[CodeBear801]

Subtask of #242, related with #321

Adjust spatialindexer/interface.go

// RankedPointInfo used to record ranking result to center point
// Distance record distance from center point to current point
// Duration records duration from center point to current point
type RankedPointInfo struct {
	PointInfo
	Distance float64
         // todo
        Duration float64
}

Modifications:

• Record Duration during ranker's calculation
  • If use OSRM, record Duration from table response
  • If use great circle distance, use length/default speed for Duration
• Record Duration in pre-processing
  • When connectivity_map build data for charge station connectivity, record Duration with Distance
• Provide Duration in RankedPointInfo interface during the implementation of StationConnectivityQuerier