Added telephone links into tag detail browser.

International phone numbers become links to IANA official URI scheme
"tel:"+number as per http://tools.ietf.org/html/rfc3966
eg: "+1 (234) 56/78-90.1 " -> "tel:+1(234)56/78-90.1"
It is not limited to key="phone"
(http://wiki.openstreetmap.org/wiki/Key:phone), so it can be used in
other keys as well.