remove multiple definition of item id

The item id exists as data attribute or as element.id postfix on multiple
elements in an article.

The basic idea is to traverse the DOM tree - starting from the event firing
element - in reverse order till an article element is found.

This article element is passed to the JavaScript functions. These JavaScript
functions are getting the elements which they want to manipulate starting from
the article utilizing the JavaScript querySelector function.

The bootstrap themes had a conflicting and unused class style definied, which is
removed by now.
do not deselect the current item if no successor/predecessors exists

When using the previous shortcut with the first article selected, the selection
is removed and no article is the current-item. Using the shortcut again, the
last article is the current-item (as expected on a new loaded page).

The same applies to the combination of last article and next shortcut.
Bookmark page: hide article if bookmark is removed

As i can't imagine any other site than the bookmarks page where an article needs
to be hidden based on the bookmark status, I've hardwired it into the javascript
function.
Translations: Remove unused, dedup and add missing entries
Update german translation