Added strings in Italian translation

Translation of:
```xml
<string name="pref_toast_show_address_title">Show address</string>
<string name="pref_toast_show_address_summary">Include the IP address in the toast notification</string>
<string name="pref_throughput_bps_title">Show traffic as bits-per-second</string>
<string name="pref_throughput_bps_summary">If selected, traffic speeds will be shown as bits-per-second; otherwise as bytes-per-second</string>
```