* Updated German translation

#350470 by hass: robots.txt content doesn't need to be passed to check_plain()

#375873 by hass: Show warning on robotstxt configuration page if "./robots.txt" file exists in webroot.

* Updated German translation

fixing compatibility note for xmlsitemap (linebreak); more efficient method of reading file contents

2. Read website root and modules directory for default robots.txt import

- read robots.txt on hook_install only
- added hook_uninstall for cleanup
- corrected some translation stings