Reuse one question dialog, backfill chat history, dim arrow icons on events

CreateQuestionDialog builds its frame once and sizes it right away from
the text's unbounded width. A frame per call broke the one-dialog guard
after the first dialog, since 1.12 binds a frame name only once. An
onclose that opens the next question runs on the next frame.

Chat history goes in with BackFillMessage, above the lines the frame
already has. SkinArrowButton dims its icon from OnEnable/OnDisable
instead of an OnUpdate per button.

modules/chat.lua

@@ -924,12 +924,9 @@ pfUI:RegisterModule("chat", function ()
 
     if not _G["ChatFrame"..i].HookAddMessage then
       if C.chat.text.history == "1" then
-        -- write history to chat
-        local history = GetChatHistory(i)
-        for j=30,0,-1 do
-          if history[j] then
-            _G["ChatFrame"..i]:AddMessage(history[j], .7,.7,.7)
-          end
+        -- write history to chat, newest first, above the lines already there
+        for _, msg in ipairs(GetChatHistory(i)) do
+          _G["ChatFrame"..i]:BackFillMessage(msg, .7,.7,.7)
         end
       end