Updated SetImageSource()

Now it loads the images into an internal dictionary, instead of
just keeping the object around.

SetImageSource() is now deprecated, but AddImageSource() and
ClearImageSource() have been added.

AddImageSource() adds a source worth of new images, but doesn't
forget existing ones.

ClearImageSource() just removes all images from the lookup.

Data/Scripts/_RichTextMgr.lua

@@ -5,7 +5,7 @@ local propEmbeddedImageTemplate = script:GetCustomProperty("EmbeddedImageTemplat
 local propEmbeddedPanelTemplate = script:GetCustomProperty("EmbeddedPanelTemplate")
 
 local fonts = require(prop_FontLookup)
-local images = nil
+local imageList = {}
 
 local API = {}
 local allFontData = {}
@@ -437,9 +437,22 @@ end
 
 
 function API.SetImageSource(obj)
-  images = obj
+  warn("RichText.SetImageSource is deprecated.  Use AddImageSource instead.")
+  API.ClearImageSources()
+  API.AddImageSource(obj)
 end
 
+function API.ClearImageSources()
+  imageList = {}
+end
+
+function API.AddImageSource(obj)
+  for k,v in pairs(obj:GetCustomProperties()) do
+    imageList[k:upper()] = v
+  end
+end
+
+
 function API.ClearText(panel)
   for k,v in pairs(panel:GetChildren()) do
     if v.clientUserData.isText then
@@ -450,12 +463,12 @@ end
 
 
 function ImageLookup(name)
-  if images ~= nil then
-    for k,v in pairs(images:GetCustomProperties()) do
-      if k:upper() == name:upper() then return v end
-    end
+  local result = imageList[name:upper()]
+  if result ~= nil then
+    return result
+  else
+    return name
   end
-  return name
 end
 
 function AsColor(str)