let everything be translatable. addded some german translations

In this pull request:
- Added missing t-functions to some stings in the templates.
- The JavaScript for showing/hiding the BB code tags was not translatable. I split the click function in two to have two distinct links that are coming from the Forum class, and show/hide the appropriate. This should finally be translated with ss.i18n in the JavaScript.
- Added some missing german translations
- Fixed some typos in the german translations
- Added some english translations for the new t-functions
- Changed the form action from '$Link(search)' to '{$Link}search' to make extension of the Forum and ForumHolder classes easier.
- Deleted the start-a-new-topic image, since images are not translatable. If desired, the image can be recreated with the use of CSS only.