logout: enbaled logout

- the application didn't call JPanel logout() methods to clear the fields
- now it calls logout() on every applicable JPanel
cusotmerPanel: fix logout

- logout didn't clear the fields properly (edit data left over)
- appears to be working fine now
productPanel: fix logout functionality

- edit fields not cleared properly on logout
- same fix as for customerPanel
SupplierPanel: fix logout functionality

- edit fields not cleared properly on logout
- same fix as for Customer and Product
UserPanel: hide "new" checkbox in user mode

- non-admins not able to create new users
- checkbox to create new users still present
- hide the checkbox for non-admins
Merge branch 'master' of ssh://github.com/d14123081/team4