Add trunk prefix and international prefix to database

[haumacher]

When calling a national number, some countries require to add a so called trunk prefix to the area code of the called number. When calling an abroad number, it is required to add some international prefix to the dial prefix of the called country. Those information differ from country to country and it would be nice, if it were available in this database. Such information could be fetched e.g. from https://www.howtocallabroad.com/codes.html