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.
Can you tell me why you have changed this? Afaik the $Link() method accent an argument of a URL slug and combines to create a final correct URL.