[0.85] #4385: Factorize massive action code in CommonDBRelation (add and remove)


git-svn-id: https://forge.indepnet.net/svn/glpi/branches/0.85-work@21528 35612d4c-9d10-0410-837c-bf9dd1be60d7
[0.85] #4385: Fix previous by specific button label


git-svn-id: https://forge.indepnet.net/svn/glpi/branches/0.85-work@21529 35612d4c-9d10-0410-837c-bf9dd1be60d7