Admin User-IP locator

Implements the step 1-3 of the [Admin User-IP-Locator spec as discussed here](https://meta.discourse.org/t/add-ip-info-lookup-for-admins/15626):

![screen shot 2014-06-15 at 18 59 20](https://cloud.githubusercontent.com/assets/40496/3281475/4ca84190-f4af-11e3-8d19-4db7e54b44b4.png)

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![screen shot 2014-06-15 at 18 58 27](https://cloud.githubusercontent.com/assets/40496/3281486/e20b9ce6-f4af-11e3-91d5-063ec4ba5007.png)


Details:
 - when an IP given, with a click on the new "lookup" button the Admin can trigger an IP-Reverse look up
 - uses ipinfo.io directly through jsonp (avoids round-trips)
 - shows hostname, location and all known details (if found)
 - automatically links long-lat to a google-maps link opening in a new window/tab
 - looks up other users also using that IP and shows them under

Notes:
 - misses copy-edit/translations (and therefore will probably fail the travis build)
 - the "No Hostname" I receive back from ipinfo as a value