Automatically add country calling code from selected country.

[ajiragroup]

While making a new lead entry, it would be better if we could select a country (a separate setting to set a default country is also a good to have feature) and type in phone number without the country code.

The system then can automatically set country code in phone number while saving. This way, using Whatsapp (which requires numbers in intl' format) would be much smooth without the need to worry missing country code while typing.