slapos_cloud: Use Cached value for getCreationDate for avoid workflow history size

When the workflow history is too big the response time
of getCreationDate is too high.

Use Cache to avoid recalculate it.

master/bt5/slapos_cloud/SkinTemplateItem/portal_skins/slapos_cloud/Base_getCachedCreationDate.py

+"""
+  When the workflow history is too big the response time
+  of getCreationDate is too high.
+
+  Use Cache to void recalculate it.
+"""
+from Products.ERP5Type.Cache import CachingMethod
+
+portal = context.getPortalObject()
+
+def getCachedCreationDate(relative_url):
+  return portal.restrictedTraverse(relative_url).getCreationDate()
+
+return CachingMethod(getCachedCreationDate,
+                     id="Base_getCachedCreationDate_",
+                     cache_factory="dms_cache_factory")(context.getRelativeUrl())

master/bt5/slapos_cloud/SkinTemplateItem/portal_skins/slapos_cloud/Base_getCachedCreationDate.xml

+<?xml version="1.0"?>
+<ZopeData>
+  <record id="1" aka="AAAAAAAAAAE=">
+    <pickle>
+      <global name="PythonScript" module="Products.PythonScripts.PythonScript"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>Script_magic</string> </key>
+            <value> <int>3</int> </value>
+        </item>
+        <item>
+            <key> <string>_bind_names</string> </key>
+            <value>
+              <object>
+                <klass>
+                  <global name="NameAssignments" module="Shared.DC.Scripts.Bindings"/>
+                </klass>
+                <tuple/>
+                <state>
+                  <dictionary>
+                    <item>
+                        <key> <string>_asgns</string> </key>
+                        <value>
+                          <dictionary>
+                            <item>
+                                <key> <string>name_container</string> </key>
+                                <value> <string>container</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_context</string> </key>
+                                <value> <string>context</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_m_self</string> </key>
+                                <value> <string>script</string> </value>
+                            </item>
+                            <item>
+                                <key> <string>name_subpath</string> </key>
+                                <value> <string>traverse_subpath</string> </value>
+                            </item>
+                          </dictionary>
+                        </value>
+                    </item>
+                  </dictionary>
+                </state>
+              </object>
+            </value>
+        </item>
+        <item>
+            <key> <string>_params</string> </key>
+            <value> <string></string> </value>
+        </item>
+        <item>
+            <key> <string>id</string> </key>
+            <value> <string>Base_getCachedCreationDate</string> </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+</ZopeData>