Beamer-friendly usage

We would like to approve the beamer usability. Therefore, we need to extend the main-container on bigger screens from 6 to 8 or 10 columns. In addition, the pixel width for changing from the full-width to a centered container should be raised to 1025px. Many beamers are still using a width of 1024 pixel and they should use the full width.

This Issue is a result of the discussion on Issue #101 (closed).