[selenium tests] Add Element IDs to Views

In order to keep the selenium code simple and robust against changes of page structure, identifiers/css-classes should be added to important elements, e.g. for the abstract submission formular.

Start by reviewing the Selenium tests and the view that renders the abstract submission form to identify which elements currently require structure-dependent selectors. Inspect the other views for similarly important elements. Done means the relevant elements have stable identifiers or CSS classes that keep Selenium selectors robust against page-structure changes.

Written by the indexing model from the issue text.