feat(rest): add password update

- as user of the rest API I can update a user's password

related to #CAM-990
Merge branch 'master' of github.com:camunda/camunda-bpm-platform
feat(rest): support group memberships

- add support for group memberships

related to #CAM-959
Merge branch 'master' of github.com:camunda/camunda-bpm-platform