[UI] Handling users and passwords

The UI does not reset passwords on startup.
Also, only the admin user is created during startup.
Then, new users can be created by the admin.
Moreover, 3 level of privileges are supported,
namely admin, tsc and lab owner.
Finally, the admin user is enabled to reset users.

JIRA: VAL-62

Signed-off-by: Ioakeim Samaras <ioakeim.samaras@ericsson.com>
Change-Id: Ie799c5b7eedf557855cccdc5a60395ec074ac381