fix(tooltip): make ElvUI tooltip style opt-in, reset for existing installs (#16)

The ElvUI tooltip style shipped on by default, so Questie restyled every
default WoW tooltip (stripping the border) for users who never asked for
it and don't run ElvUI. Default is now false, plus migration [8] resets
it off once for existing profiles.

Modules/Migration.lua

@@ -119,6 +119,13 @@ local migrationFunctions = {
         if Questie.db and Questie.db.global and Questie.db.global.learnedData then
              Questie.db.global.learnedData = nil
         end
+    end,
+    [8] = function()
+        -- The "ElvUI style tooltips" option shipped enabled by default, which made Questie
+        -- restyle every default WoW tooltip (stripping the border) for users who never asked
+        -- for it (#16). It is now opt-in (default false). Reset it off once so existing installs
+        -- get their default tooltips back; users who want the flat style can re-enable it.
+        Questie.db.profile.elvuiStyleTooltips = false
     end
 }