dms_ui_test: test for implicit sucessor/predecessor fields

note that the test documents are a bit "easy", the HTML references a web
page, but also in the html text we have the reference of the image,
because when we index html in full text we don't index images URLs.
That's a bit like hiding a bug, but testing this is not the purpose of
this test (here we are testing UI only)
Status Job ID Name Coverage
failed ERP5.CodingStyleTest-TestRunner1


passed ERP5.PerformanceTest-TestRunner1