Add coutry code selection in registration

[s-yanev]

Is your feature request related to a problem? Please describe.
On the registrion screen there is no possible way to select my country code.

Describe the solution you'd like
On the registration screen where the phone number is set, add drop down menu for country code selection. A single item in the drop down should include in it the country name and the phone code e.g. Bulgaria(+359).