Add an interface (implemented by the Part) for controlling the really basic document viewer functionalities. This (along with a small refactor in the okular shell) gives the user the possibility to start okular with:
  -p, --page <page> : to select the startup page
      --presentation : to start directly in presentation mode
implementing also KPDF wishes #134115 and #137905.

svn path=/trunk/playground/graphics/okular/; revision=619681