Added 'samba' role

- using 'samba' role you can install and configure Samba 3 service;

- configuration is stored in hash variables and converted in smb.conf
  template by a Jinja2 macro;

- by default public, read only share is created. 'samba' role does not
  create share directories by itself, you can use 'directories' role to do
  that, and specify custom owner, group and permissions;

- by default, each user has his/her own home directory created by
  a shell script. You need to add users separately using 'smbpassword'.
  Unix and Samba passwords are not synchronized, Unix and Samba home
  directories are separate;

- printer support is disabled by default;