Owner has all user permissions

closes #3075
- added special treatment for role with name ‚Owner‘
Move post slug endpoint & add endpoints for users

closes #3187

- move slug endpoint to post/slug/:slug
- create similar  slug and email endpoint for users
- add/update tests
Merge pull request #3227 from sebgie/issue#3075

Owner has all user permissions
Merge pull request #3223 from ErisDS/issue-3187

Move post slug endpoint & add endpoints for users