Shortcuts: Single page - Enhanced CSS

Followowing changes:
 * sourced out the shortcuts to a own page 
 * removed old shortcuts from basic-help page
 * Added action mode shortcuts to new page
 * Introduced <kbd> tags from http://michaelhue.com/keyscss into blogs.css to get better presentation of keys on the shortcuts page
 * Correct links to Shortcuts (CHM-administrative files, basic_help.html)

If you like the representation of keys, it should be applied all over the documentation