xfd: warn when renominating pages with a recently closed xfd

[NovemLinguae]

Requested by Awesome Aasim at https://en.wikipedia.org/wiki/Wikipedia_talk:Twinkle#Can_we_have_a_warning_for_renominating_pages_where_the_discussion_was_recently_closed%3F

Possible algorithm:

• via ajax, when the xfd module is loaded
• check the talk page for {{Old XfD multi}}. parse its contents. see if there's been any XFDs closed within the last month
• if so, display a string in red font with the message "Warning: This page was was recently nominated for deletion and had its discussion closed. Please take caution before renominating again."