Avoid encoding issues by fetching GeoIP cookie through jquery.cookie

In EventLogging Geo.country gets stored, and there we saw country
values like

  GeoIP%3D%3A%3A%3A%3Avx; mediaWiki.user.sessionId=<SESSION_ID_REMOVED>; GeoIP=
  US%3A<CITY_REMOVED>%3A<LAT_REMOVED>%3A<LON_REMOVED>%3Av4; ve-beta-welcome-dialog=1; centralnotice_bucket=0-4.2; GeoIP=CH

(replaced potentially harmfull data by <..._REMOVED>) where encoded
“=” (%3D) and “:” (%3A) lead to misparsings country values. Sometimes,
the country values contained GeoIP= in them, sometimes more than
once. Sometimes, even sensitive data as session ids were present.

By using jquery.cookie, we let the library take care of isolating the
relevant part of the cookie and decoding it.

Bug: 66478
Change-Id: Icc39496c3a0ebeabb6166b5250d0358f1b022d63