erp5_corporate_identity: Set missing http_cache on skins

bt5/erp5_corporate_identity/SkinTemplateItem/portal_skins/erp5_corporate_identity/template_images/fallback.png.xml

@@ -6,6 +6,10 @@
     </pickle>
     <pickle>
       <dictionary>
+        <item>
+            <key> <string>_Cacheable__manager_id</string> </key>
+            <value> <string>http_cache</string> </value>
+        </item>
         <item>
             <key> <string>__name__</string> </key>
             <value> <string>fallback.png</string> </value>

bt5/erp5_corporate_identity/SkinTemplateItem/portal_skins/erp5_corporate_identity/template_images/recycle.png.xml

@@ -6,6 +6,10 @@
     </pickle>
     <pickle>
       <dictionary>
+        <item>
+            <key> <string>_Cacheable__manager_id</string> </key>
+            <value> <string>http_cache</string> </value>
+        </item>
         <item>
             <key> <string>__name__</string> </key>
             <value> <string>recycle.png</string> </value>

bt5/erp5_corporate_identity/SkinTemplateItem/portal_skins/erp5_corporate_identity/template_images/slide_icon.png.xml

@@ -6,6 +6,10 @@
     </pickle>
     <pickle>
       <dictionary>
+        <item>
+            <key> <string>_Cacheable__manager_id</string> </key>
+            <value> <string>http_cache</string> </value>
+        </item>
         <item>
             <key> <string>__name__</string> </key>
             <value> <string>slide_icon.png</string> </value>

bt5/erp5_corporate_identity/SkinTemplateItem/portal_skins/erp5_corporate_identity/template_themes/themes.css.xml

@@ -6,6 +6,10 @@
     </pickle>
     <pickle>
       <dictionary>
+        <item>
+            <key> <string>_Cacheable__manager_id</string> </key>
+            <value> <string>http_cache</string> </value>
+        </item>
         <item>
             <key> <string>__name__</string> </key>
             <value> <string>themes.css</string> </value>