xmlui: Use CloudFlare's CDN for jQuery instead of Google's

CloudFlare's CDN is 3 less hops away from Nairobi than Google's, and
5 less than from the East coast of the US.  Also, CloudFlare's CDN
has better TLS support, see this presentation from Google Engineer
Ilya Grigorik:

    https://docs.google.com/presentation/d/1l9c9ROjLTD8clOL0yFufAOMbxNC0D-19zCiXMgqtY-M/present?slide=id.p19

Replaced all using sed:

    find dspace/modules/xmlui/src/main/webapp/themes/ -iname "page-structure.xsl" -exec sed -i 's/ajax.googleapis.com/cdnjs.cloudflare.com/' {} \;

Signed-off-by: Alan Orth <a.orth@cgiar.org>