Prevent multiple prompts for the root password in Nutty

Currently, Nutty asks for the sudo privilege password every time the user interacts with a feature in Nutty that requires root privileges. This is because gksudo is invoked for every action requiring root privileges.

Polkit will be replacing gksudo for commands that require root privileges. a policy file for nutty will define the actions and <allow_active>auth_admin_keep</allow_active> will be used to keep the admin privileges for a short time. this will prevent the dialog asking for password to come up every time the user executes the action and will only come up for the first time