Bug 19817: (QA follow-up) Add German manual and fix system preference help files

Bug 19817: (QA follow-up) Add German manual and fix system preference help files

- German language manuals were added since this patch was started
- The structure of the manual was changed slightly, system
  preferences were moved into their own chapter

To test:
- Test help files display correctly for system preferences display correctly
  Note: Local use uses a different page than the other tabs
- Test German shows up as option in KohaManualLanguage and links
  correctly

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>