Adjusted site selector widget to site groups

(bug 51560) In the site selector's input box and the corresponding suggestion list,
the site id is shown instead of the language code now. (The matching mechanism is
using the site id already.) Matching the language code is reimplemented with this
change set.

Change-Id: I911b4a8e9871f426580be1100b004740ec9b9916
Merge "Adjusted site selector widget to site groups"