Explicitely surcharge some skins in a specific skin folder (to follow http://www.erp5.org/Discussion/GuidelinesForFieldLibrary#Exception).

Remove skin_priority from erp5_dms as it now become useless.

git-svn-id: https://svn.erp5.org/repos/public/erp5/trunk@35690 20353a03-c40f-0410-a6d1-a30d3c3de9de