Automatically pass desired changeset comment to iD editor

This will help iD users to follow HOT's changeset comment requirements - they won't have to remember to fill in the comment box as it will automatically do it for them.

NOTE: the iD side of it is done <https://github.com/openstreetmap/iD/issues/2311>
and is not yet live on OSM website, but will be when next iD version
comes out.