Selecting devices to watch

- Now you can select which devices will track for disk usage (always
sum all devices in one)
- Watch for changes in devices (Plug & Unplug)
- Added menu item for manage disks
- Fixed a bug when the speed is equals or more than 1GB/s, the app
throw an Exception and closes
- BUG: When a device is Plugged or Unplugged the speed is incorrect