crm: Associate MailMessageConstraint to Mail Message

Since sending email will not work without destination email, we can globally set this constaint

bt5/erp5_crm/PortalTypePropertySheetTemplateItem/property_sheet_list.xml

@@ -6,6 +6,9 @@
  <portal_type id="Event Path">
   <item>EventPath</item>
  </portal_type>
+ <portal_type id="Mail Message">
+  <item>MailMessageConstraint</item>
+ </portal_type>
  <portal_type id="Meeting">
   <item>DefaultEventPath</item>
  </portal_type>

bt5/erp5_crm/bt/template_portal_type_property_sheet_list

 Campaign | DefaultEventPath
 Campaign | DefaultOutcomePath
 Event Path | EventPath
+Mail Message | MailMessageConstraint
 Meeting | DefaultEventPath
 Support Request | Codification
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