Allow swapping of origin/destination in DT

[hbruch]

Digitransit supports to enable swapping the origin and destination text fields' content via showMultiPointControls config.

See e.g. for the opas.matka.fi instance:

However, in our fork, this stil enables the viaPointControl, which is currently not supported by OTP. Upstream digitransit has been changed to reflect this. These changes should be backported and swapping should be enabled.