Add blue button as "makpi" viewer-link for relations

[sun-geo]

It seems for the iD-Editor a "Mapki" viewer link will not implemented at the moment, see issue: openstreetmap/iD#6202

Therefore, maybe it would be possible to add Mapki-viewer to PeWu relation tab.

current view without mapki:

potential new view with mapki:

The background why I would like to have this integrated is, because mapki has nice overview about relation members for the different object versions, for example see here:
http://osm.mapki.com/history/relation.php?id=5686711

[sun-geo]

or yellow button, actually the colour doesn't matter for me ;-)

[sun-geo]

Thank you :-)