Review User roles and permissions

[lislis]

• user can: create and update cases
• reviewer can: delete cases, set review status
• moderator can: publish data, configure data structure, invite new users, block and remove users, set user user role except for admin
• admin can: ?

[lislis]

• [ ] refactor to use cancancan https://github.com/CanCanCommunity/cancancan
• [ ] define list of abilities for cancancan

[lislis]

• [ ] research if/ how jwt ('token claims') and cancancan can cooperate