Feature crud for users

see https://github.com/9ci/grails-angle-grinder/pull/24

- [x] create list (with grid)
- [x] create show action
- [x] add delete button inside the show view
- [x] edit action
- [x] add edit button inside the show view
- [x] create action
- [x] cancel button on the edit page
- [x] cancel button on the create page
- [x] delete action
- [x] show on click inside the grid's row