Add --no-run parameter

This parameter allows e.g. to synchronize the database without starting
the webserver.
Add command to backup the database
Add a simple wxPython based gui frontend for openslides
Update portable to use new gui frontend

 - switch portable to use gui frontend

 - add version resource and icon to portable

 - Regenerate openslides.exe
Merge pull request #698 from andkit/exp-gui

Gui frontend for openslides