German documentation: Insert short comment on HTML in agenda text fields (fixed #808).
Rename visual strings of permissions: Add plural s (fix #797). Also update all language files.
Merge pull request #813 from normanjaeckel/RenamePermissions

Rename visual strings of permissions
Merge pull request #812 from normanjaeckel/UpdateDoc

German documentation: Insert short comment on HTML in agenda text fields...
Updated German translation (some typos).