Some bug fixing for 1.5b1

- Fixed #921 (Check THANKS URL for jQuery UI Nested Sortable)
- Fixed #919 (Permission problem in agenda)
- Fixed #918 (Search does not work for guest users)
- Fixed search-bar position.
- Updated EN po files.
Merge pull request #928 from emanuelschuetze/1.5-fixes

Fixes for 1.5b1