If the new $wgThanksConfirmationRequired global variable is true,
require users to confirm that they want to send thanks.
Bug: 47658
Change-Id: I4663844a324a2797917b027ceb1c8c07b1e180d5
Thanked revision to be stored both server side in the session and client side
in a cookie. Thanked revisions found in either storage solution will replace
their 'thank' link with the string 'thanked'.
Bug: 46690
Change-Id: I976cd8fbf00856c67b77daeb0d0a952efb371661