XWIKI-15198: Skin logo doesn't change with the new Color Theme

* Added a translation to contain the warning for users.
* Added this warning

Note: I tried to have it not inline, but it did not work properly together with the definition list syntax.

xwiki-platform-core/xwiki-platform-skin/xwiki-platform-skin-ui/src/main/resources/SkinsCode/Translations.xml

@@ -38,6 +38,7 @@
   <hidden>true</hidden>
   <content>skin.sheet.title=Skin
 skin.sheet.properties=Skin Properties
+skin.sheet.properties.logo.warning=This logo is usually overridden by the one defined in the color theme. If you want to change the wiki logo, consider editing the current color theme instead.
 skin.sheet.deprecatedProperties=Deprecated properties
 skin.sheet.overriddenTemplates=Overridden templates
 skin.sheet.addTemplate=Add a new overriding template

xwiki-platform-core/xwiki-platform-skin/xwiki-platform-skin-ui/src/main/resources/SkinsCode/XWikiSkinsSheet.xml

@@ -81,8 +81,8 @@
   #foreach ($prop in $class.properties)
     #if ($prop.classType != 'TextArea')
     ; {{html}}<label for="${className}_$escapetool.xml($doc.getObject($className).getNumber())_$escapetool.xml($prop.name)">$escapetool.xml($prop.prettyName)</label>{{/html}}
-    : #if($prop.name == 'logo')## Avoid line break
-      {{attachmentSelector classname="${className}" property="${services.rendering.escape($prop.name, 'xwiki/2.1')}" filter="png,jpg,gif,svg" displayImage="true"/}}## Avoid line break
+    : #if($prop.name == 'logo'){{warning}}{{translation key="skin.sheet.properties.logo.warning" /}}{{/warning}}\\\\## Avoid line break for the definition list
+    {{attachmentSelector classname="${className}" property="${services.rendering.escape($prop.name, 'xwiki/2.1')}" filter="png,jpg,gif,svg" displayImage="true"/}}
     #else$doc.display($prop.name)#end
 
     #else