Specify isochrone `range` separately for each location

[koebi]

This results from the original documentation of the range parameter mentioned in #882.

Currently isochrone endpoint supports multiple locations, but will apply the same range(s) to all of them. It might be useful to be able to specify ranges for each location separately.

Possible implementations are

1. the range parameter accepts an array of arrays of range values if multiple locations are given. Each array specifies the ranges for one of the locations, in order
2. an array of range values given to the range parameter sets a maximum range for each location separately. The interval parameter could be used to specify intermediate ranges.

[jayaddison]

This would be an API-breaking change, but another idea could be to reconsider the concept of locations in IsochroneRequests.

It's nice that the API supports multiple locations, but correlating two request parameters (i.e. knowing that location at index 0 corresponds to range at index 0) could be a little fragile or confusing for clients.

One suggestion to make the connection more explicit would be to bundle the range and location into the same object. In that case they'd become more like a queryLocation.

# IsochronesRequest
{
  "queryLocations": [
    {
      "location": [8.681495,49.41461],[8.686507,49.41943],
      "range": [200,300]
    },
    {
      "location": [7.681495,49.41461],[7.686507,49.41943],
      "range": [100,200]
    },
    ...
  ]
}

(if so, there could be practical implementation details -- and performance / resource consumption considerations -- as a result of allowing varied combinations of queries in a single request, but perhaps they're better handled generically at a lower level using per-request resource governance or something along those lines)