Ability to set admins

As an Owner I'd like to add other users into Admins so that I can share administration responsibility with others

Acceptance Criteria

• Under Administration menu there should be Users menu item. Only Admins can see that.
• After pressing it, user gets to the list of users registered in Antarcticle.
• Each row should have username, first name, last name and a column Roles.
• There should be 50 users per page. Search box should search by username/first name/last name (search should be case-insensitive, without suggestion list)
• At the moment there should be 2 roles: User & Admin. A combo box should give a possibility to choose between them.
• After a role is chosen, it should be automatically applied (no Save/Cancel buttons). Some visual effect (green mark, popup, etc) should state a successful end of operation.
• If the role wasn't changed successful (e.g. no connection to server or someone has revoked admin role from the current user), a red popup should explain the error.
• If user was provided with an Admin role, then he can do the same stuff as current admin: editing/removing others articles/comments and see Administration menu.
• User cannot change its own role.
• If user tries to enter a direct address of the page but he has no permissions, he should get 403 Forbidden (and status code should also be 403).