Changed adding apt_key
Added 'avahi' task in 'tweak' role
Added 'virtualbox' role
Added new tasks to 'tweak' role
Added 'smartmontools' role
Added 'tlp' role
Fixed syntax
Added Debian's settings for 'tlp' role
Changed variable's name
Changed variable's default value
Added 'grub' role
Added 'p7zip' role
Added 'indicator_multiload', 'indicator_sensors' role
Fixed syntax
Deleted unused file
Deleted unused tasks
Add 'faenza-icon-theme'
Add 'dropbox' role
Add 'gnome_commander' role
Fix variables' name in roles: 'pre_packages', 'post_packages'