control bar: allow multiple usage on page

Created by: spoeschel

The control bar in /contrib/akamai/controlbar currently uses hardcoded element names for all bar elements. Hence one can only use a single bar instance on a particular HTML page.

It would be great to e.g. be able to specify an optional suffix that is then appended to every element name when creating a control bar, in order to support multiple bars (and of course videos) on one page.