Fix redirection after adding or removing a relation

After adding or removing a statement, the method returns "document_relations".

Then, depending on the plugins installed, the user is redirected to

• http://localhost:8080/nuxeo/document_relations.faces, which displays the Relations tab
• http://localhost:8080/nuxeo/default/nxpath/path/to/my/doc@document_relations?mainTabId=MAIN_TABS%3Adocuments&conversationId=0NXMAIN&tabIds=MAIN_TABS%3Adocuments%2C%3ATAB_RELATIONS which display a Page Not Found error

See NXP-10587 to understand why there are two different behaviors.