Add a Talents skin entry with an enable switch and per-window scale

The talent window, the Vanity and Wardrobe windows it switches between and
the tab row along its bottom are one feature to the player, so they get one
entry in the Skins tree and one master switch gating all three
Initialize calls together. Skinning one of them without the others reads as
a bug.

Scale is a slider per window, 0.5 to 1.5, applied as a multiplier on the
existing scale rather than an absolute -- the three don't ship at the same
size (the vanity store's frame runs about 9% larger than the others), and
that is the server's choice to keep. A setting of 1.0 leaves everything
exactly as it was.

The scale is set on Collections, not on the window itself. All three
windows and the tab row are its children, and it is the only one of them
with mouse enabled -- it is what the player drags. Scaling a window
directly left the drag target at full size, so a shrunk window had to be
grabbed by clicking outside itself, and the tab row, not being a child of
any window, kept whichever size the first-opened one gave it. Scaling the
container moves its hit area with it and the tabs follow as children.

Modules/WardrobeFrame.lua

@@ -52,6 +52,10 @@ local function SkinCategoryTabs()
 end
 
 local function SkinContents()
+	-- Scale is set on the shared container while this window is the open one,
+	-- which carries the tab row along with it (see Skinning.lua).
+	Skin:ApplyWindowScale("wardrobeScale")
+	Skin:CollectionTabs(_G[FRAME_NAME])
 	Skin:Title(_G[FRAME_NAME.."TitleText"])
 	Skin:CloseButton(_G[FRAME_NAME.."CloseButton"])
 	SkinActionButtons()