Czech translation

I have added some missing Czech translation but I am not able to fork the repo here on git.ispconfig.org (and so create a Merge request).

I have clone the ispconfig3 repository to github and make some commits (61b6df14..6a1eb0488) there. Can anyone review and merge it to the upstream? I have created a pull request there if it comes handy.

I am able to format-patch the commits if needed.