[Tagging] Unification of google-plus links

[Andreas Goss]

> I don't want to change the addr:-, website-, phone-, fax- or
> email-key!!! I never said it.

As Tobias pointed out, we have to look at the bigger pucture. Why use 
contact: here, when it's not used by the majority anywhere else.

> The contact-namespace associate, that the defined facebook- or
> googleplus-page are a medium to communicate with the defined object. I
> know a lot facebook-pages, who are created from fans or generated from a
> wikipedia-pages. That are mostly not a communication channel.

But those unofficial (fan) pages should not be linked anyway. It would 
always be the official page.

In addition even a lot of those pages are not really used for 
communication, so that seems even more like a argument against contact:, 
especially as mappers are not going to first figure out which company 
replies on google+ and which doesn't.
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openstreetmap.org/user/AndiG88
wiki.openstreetmap.org/wiki/User:AndiG88‎