core: split "edit code" logic in a new bt

erp5_core should contain only the minimal objects needed during
bootstrap phases to install other business templates, but it also
contained all the user interface to edit and maintain the code, run test
and all of this is not strictly required at this point.

bt5/erp5_ide/SkinTemplateItem/portal_skins/erp5_ide.xml

+<?xml version="1.0"?>
+<ZopeData>
+  <record id="1" aka="AAAAAAAAAAE=">
+    <pickle>
+      <global name="Folder" module="OFS.Folder"/>
+    </pickle>
+    <pickle>
+      <dictionary>
+        <item>
+            <key> <string>_objects</string> </key>
+            <value>
+              <tuple/>
+            </value>
+        </item>
+        <item>
+            <key> <string>id</string> </key>
+            <value> <string>erp5_ide</string> </value>
+        </item>
+        <item>
+            <key> <string>title</string> </key>
+            <value> <string></string> </value>
+        </item>
+      </dictionary>
+    </pickle>
+  </record>
+</ZopeData>