Delete entire boards from DataBoards when cleaning it gives us a 404.

This would happen when a board gets deleted, like /s4s/ hopefully one day.

src/databoard.coffee

@@ -65,6 +65,10 @@ class DataBoard
     $.set @key, @data
   ajaxClean: (boardID) ->
     $.ajax "//api.4chan.org/#{boardID}/threads.json", onload: (e) =>
+      if e.target.status is 404
+        # Deleted board.
+        @delete boardID
+      else if e.target.status is 200
         board   = @data.boards[boardID]
         threads = {}
         for page in JSON.parse e.target.response