Administrator can adjust a user's rights

[catalry]

Is your feature request related to a problem? Please describe.
Currently, the system offers only one admin. The admin user should be able to grant/remove admin rights to other users.

Describe the solution you'd like
An administration tab should be implemented in order to allow the following use case:

1. Administrator logs into Easyshare.
2. Administrator accesses the Easyshare admin tab.
3. Administrator searches for a specific user.
4. Administrator changes the user's admin rights.

Describe alternatives you've considered
/

Additional context
/