Add pfUI-native macro icon picker

Replace Blizzard's MacroPopupFrame (the name + icon dialog) with a
custom pfUI picker driven by IconDataProviderMixin, so the full spell +
item + loose icon set is available instead of the stock spell-only list.
It has a searchable, filterable icon grid and saves through
C_Macro.CreateMacro / C_Macro.EditMacro, which take the icon as a texture
string -- so arbitrary icons (including index-less INV_* item icons)
persist. The macro-frame API is identical on the modern (Turtle/Octo)
and stock-vanilla macro UIs, so the picker works on both with no client
detection.

The new macroicons module takes over the New / Change-Icon buttons and
retires the stock popup; the blizzard macro skin now only skins
MacroPopupFrame when that module is disabled.

init/modules.xml

@@ -71,6 +71,7 @@
   <Include file="..\modules\energytick.lua"/>
   <Include file="..\modules\totems.lua"/>
   <Include file="..\modules\macrotweak.lua"/>
+  <Include file="..\modules\macroicons.lua"/>
   <Include file="..\modules\turtle-wow.lua"/>
   <Include file="..\modules\superwow.lua"/>
   <Include file="..\modules\innervatecall.lua"/>